Interesting newly discovered cabling method, with surprisingly good results.
I'm still working on how to best put together all the sources and processors in my configuration.
(1) I've now tried and rejected the "AVR HDMI1-out -> splitter" method, because it loses HDMI-CEC and eARC, things which are important to me.
(2) I've also tried and rejected the "AVR HDMI2-out -> A16 -> HD Fury Dr. HDMI 4K (dead-end)" because that simply did not work at all. It's been suggested that if I add a "dummy head" HDMI plug into the OUTPUT of the DH4K (because it should NOT be dead-ended) that this might solve the problem. Haven't bought one of the dummy head items yet (inexpensive $8) to try, but I don't think I will.
(3) The HD Fury support thread over on AVS Forum suggested that the DH4K (at about $150 delivered) was not the proper device to be using for my objective. They suggested that their Vertex 2 (priced at almost $500 delivered) would almost certainly do the trick. I'm not interested.
So in the end I'm back to where I started, using a combination of HDMI and analog inputs on the AVR, along with having my streaming devices feeding three of the HDMI inputs on the A16, with the one HDMI output from the A16 going to HDMI3-in of the AVR. HDMI1-out of the AVR goes to my LG C9 TV. My Oppo 203 has its HDMI MAIN-out (for video only) going to HDMI2-in of the AVR. Its second HDMI2-out (for audio only, delivering bitstream) goes to HDMI1-in of the A16. This setup automatically supports getting headphone audio output from the A16 for all four of my sources, all of which have audio via HDMI going into the A16. Video from the three streaming devices (which are also delivering their audio directly to the A16 on the way through) goes through the A16 and into the AVR, and then out to the TV. Video from the 203 goes directly into the AVR and then out to the TV, with multi-channel bitstream audio going to the A16 for headphone listening.
So for headphone listening via A16 there's nothing to discuss. But now we talk about the alternative of wanting to listen to sound "casually" and analog, using my 2.0 speakers along with "tone control" provided by my DBX 14/10 EQ. Sound from my [pretty good] 2.0 speakers with tone control via the 14-band DBX EQ is much superior to the very basic and simple +/- 6db bass/treble control available from the AVR, and so I really do want to use it for ANYTHING coming out of my 2.0 speakers (which are managed by the AVR).
And herein lies the latest knowledge breakthrough. The A16 provides various ways to deliver output audio, but unfortunately "AV" mode (and then pushing the SPEAKER button on the remote) delivers the input multi-channel audio directly to the output analog outputs but provides no way for AV mode to downmix it to 2.0 stereo (i.e. to just the Lf/Rf analog outputs, like the "2ch-stereo" mode of an AVR). So unless the source audio is itself only 2.0, feeding the L/R analog outputs of the A16 to the analog audio input of the AVR results in only hearing the Lf/Rf channels of a multi-channel source. Not acceptable.
Alternatively, the A16 also provides "stereo mixdown", but not for its AV-mode feeding its analog outputs. It only provides stereo mixdown for headphone output, with several additional options. When stereo mixdown to 2.0 is properly activated on the A16 you can use the "headphone" button on the remote to apply the SVS processing to that 2.0 stereo mixdown delivered to the headphone output (both analog and optical). And you can also use the "speaker" button on the remote to inhibit SVS processing, and simply provide what is really "2ch-stereo" pure unprocessed stereo mixdown and delivered to the headphone output (both analog and optical).
And even furthermore, you can optionally apply (or not) your HPEQ to the stereo mixdown, in both modes of either SVS-applied or SVS-inhibited. So what you hear through headphones is absolutely a stereo mixdown, presented through the "2.0 PCM listening room using some PRIR to define the 2.0 speakers being used". And furthermore you can apply SVS or just pass-through the 2ch-stereo downmix as-is (with no SVS processing). And furthemore you can optionally apply the equalization appropriate for the headphones you're using by activating its HPEQ or not. Again, all terrific... if you are listening through headphones.
But what I discovered is that I can actually NOT use headphones to listen but instead use my 2.0 speakers, managed by the AVR, for this very 2.0 stereo mixdown from the A16 that was intended for headphones. And furthermore I can even insert my DBX EQ into the audio path, so that the sound delivered on my 2.0 speakers from the AVR is tone-controlled by the EQ as I want.
The trick is that I use an external DAC fed via optical cable from the A16, normally for handling the still-digital SVS-processed headphone output. The analog output of the DAC is then sent via XLR cable to my Stax amp/headphones, for my listening pleasure using headphones. Well as it turns out the DAC also has RCA outputs (in addition to the XLR outputs), so I can simply feed the RCA 2.0 stereo analog output from the DAC into the L/R analog input of the DBX EQ. And then I can feed the L/R analog output of the DBX EQ into an analog input of the AVR. And I can configure the AVR to combine the input HDMI-provided video coming directly from the HDMI-output of the A16 with this analog L/R stereo audio (tone controlled by the DBX EQ) coming by way ot the optical headphone output of the A16 -> DAC -> RCA to DBX EQ -> AVR.
So, what am I actually now hearing on the 2.0 speakers? It is exactly what would normally be heard through headphones out of the A16. If I am NOT using "stereo mixdown" mode then it is actually the genuine multi-channel multi-speaker SVS-processed simulated PRIR-defined listening environment as my ears would hear it through headphones, but delivered in my ordinary bedroom through 2.0 speakers on the floor. Remarkably, it sounds very much like the AIX listening room defined by the PRIR. There absolutely is that same 3D-like sensation you get when listening through headphones, even though the 2.0 speakers are not really appropriate for the HPEQ being applied. Nevertheless it is remarkably good! Definitely a sensation of "depth" around the TV screen, like there were more than just the 2.0 speakers... like in the AIX room for real. Most importantly I am also utilizing my DBX EQ for additional tone control (beyond what the A16 and PRIR and HPEQ are already applying to this headphone-out feed).
Alternatively, I can instead go to official "stereo mixdown" mode. This changes the headphone feed to now reflect only 2.0 channels as the source, and then either with or without SVS processing on top of it, and then either with or without HPEQ applied (I have disabled this since I'm clearly not listening through headphones). This is exactly how it would sound if I put on the headphones and listened, except that it is coming out of my 2.0 speakers (again by way of the A16 optical -> DAC -> RCA -> DBX EQ -> AVR). And I can say that it is EXACTLY AS YOU'D EXPECT, from speakers instead of headphones! If I set it to stereo mixdown WITH SVS-applied, it sounds a bit 3D-like but nothing like the earlier presentation without using stereo mixdown but simply feeding 2.0 speakers instead of real headphones. But if I then turn off SVS completely, and deliver "pure 2ch-stereo" mixdown to the 2.0 speakers, it sounds FLAT and simply 2D, i.e. L/R! Really no sensation of depth at all. The sound is simply flat at the vertical plane of the 2.0 speakers and goes no "deeper" or "in-front".
So this is really quite a revelation. And the above story is for the three streaming source devices going into HDMI2-4 of the A16. But it also applies to HDMI1, where the multi-channel bitstream audio coming from the Oppo 203 is provided. There is no video here that needs to be passed through to the AVR, and besides the MAIN-out of the 203 (for video only) is separately going into HDMI2-in of the AVR. So the AVR is not expecting 203 video to be coming from the A16. However since there is an HDMI connection from 203 to the A16, I can also do the same set of stereo mixdown (or not) delivery methods out via A16 optical -> DAC -> RCA -> DBX EQ -> AVR to the 2.0 speakers for any audio coming from the 203. All well and good, but it requires that the A16 be powered on. When "casually" watching/listening to HDTV (which is fed through the external HDMI input of the 203) I really just want the 203 and AVR (to handle the speakers) powered on. I don't want or need the A16 on unless i want to listen through headphones.
So in this case I have the speaker configuration on the 203 set to 2.0 speakers, so the 203 itself is doing 2ch-stereo mixdown for analog audio presented on its own L/R line-outputs. And I have these two L/R analog outputs connected to a second L/R input on the DBX EQ (separate from the first L/R input which accepts RCA output from the DAC as I described earlier). I simply have to push the INPUT 1/2 button on the DBX EQ to accept the 203's stereo mixdown feed and pass it on to the AVR, and I'm now listening to HDTV audio (as 2.0 stereo mixdown). Yes, it is "flat" (since there is no A16 and SVS involved), but it's perfectly acceptable. And it does make use of the DBX EQ for tone control, which is the objective.
This, then, is my now current configuration. No cables need to be moved except for eARC for a TV app, and even then only if I want to listen through A16 and headphones, or DBX EQ tone control for audio through 2.0 speakers, because I can get "normal" eARC audio directly from the AVR (but without benefit of the DBX EQ) exactly from the cable to the TV connected to HDMI1-out of the AVR. But otherwise, for all NON-eARC situations (which is 99.5% of my operation) this cabling provides 100% of what I want.
(a) A16 and DAC is only powered on when needed, meaning (a) when I want to listen through headphones, or (b) when I want to listen through speakers in A16-facilitated SVS mode (i.e. simulating the AIX room but using 2.0 speakers instead of 2.0 headphones), or in official 2.0 stereo mixdown mode (either with or without SVS applied). DBX EQ is only powered on if 2.0 speakers are used. And actually the AVR only needs to be powered on if I am listening through speakers. Because of its HDMI Standby-through feature it doesn't need to be powered on if I'm listening through headphones to a streaming device source, which passes video out the A16 and into the AVR and out of it... even while the AVR is in standby mode.
(b) Casual HDTV listening via 203 (i.e. through speakers) does not require the A16 and DAC to be powered on. Stereo mixdown is done by the 203 and still feeds the DBX EQ which feeds the AVR. So the AVR, DBX EQ and 203 must be powered on when speakers are needed. Only when headphone listening to something from the 203 is desired (either discs or HDTV) does the A16 and DAC need to be powered on. But then the DBX EQ can be powered off (since speakers are not being used) and even the AVR can be powered off, again because of its HDMI Standby-through feature that will pass video coming from the 203 on through and out to the TV, even while the AVR is in standby mode.
NOTE: while I am blessed to have a DBX 14/10 EQ to improve tone control for analog sound from my 2.0 speakers, that's just a goodie. Not required in order for this cabling approach to work. What is required, however, would seem to be the external DAC that has TWO ANALOG OUTPUTS: (a) XLR to the amp/headphone for headphone listening, and (b) RCA to an analog input to the AVR for feeding the 2.0 speakers (either with or without an EQ in the middle). I haven't used the built-in headphone outputs of the A16 but perhaps the front and rear analog headphone outputs could also be used to feed the two output path options, i.e. (a) to true headphones, and (b) to AVR analog input in order to support speakers.
Definite advantage of having an AVR.
