If you are referring to the gain switch on the rear of the unit, it appears to be ONLY for the RCA input. It will have no effect on anything coming through the DAC or XLR inputs.
By the way, the CD that comes with the HDVD800 that contains the USB driver for Windows also contains the "Instruction Manual", so if you have a Mac, the CD is still useful
Although pretty thin in useful information it does contain text discussing some things that I've not seen elsewhere (such as about 5 or 6 lines of description on setting the RCA gain control.
I was going to just copy the picture from the manual to here but I didn't know what kind of copyrights there might be. There were no copyright markings in the manual but if they are being so tight lipped about technical info, then who knows what might come of it?
Here are some other interesting tidbits I got from the manual and the specification page:
1) There is a section that states "We recommend using high-impedance headphones for an optimal listening experience". Also the spec page refers to 600 ohm loads for the headphone outputs.
2) Another part says to "Connect one or several headphones" and it shows up to 4 headphones being simultaneously connected. So what **I** want to know is, are those jacks all isolated from each other or are they just gang bussed and hardwired together. If the latter is the case, then plugging in multiple phones will effect the sound quality. In an amp of this presumed quality and cost, isolated outputs would be expected, but I'm suspecting that it is not so, especially considering item #3 below.
3) The S/PDIF (coax/optical) maximum sample rate is only 88.2 KHz! This is also a bit suspicious. So in order to avoid jitter issues, you should be using the USB interface because it is likely using Asynchronous instead of adaptive mode transfers. Maybe cost cutting by not putting in any rigorous clock recovery circuitry on S/PDIF when you "should just use the better async mode" supported on the USB interface? Note that the AES/EBU input appears to be still listed as having all sampling rates (44.1, 48, 88.2, 96, 176.4, and 192 KHz).
Anyway, it kind of appears that if you want to use hi-rez audio tracks, don't plan on using TOSlink to connect to the HDVD800. This kinda ticks me off as I wanted to occasionally reposition my HDVD800 next to my bed running a 26 foot medical grade glass optical TOSlink to my computer. Now I'll have to reconfigure to downsample all my 24/96 and 24/192 files to 24/48 just to get them over the TOSlink. And this all in a $2K DAC/amp?
Also, when looking at the DAC capabilities as reported through my iMac's midi control, it shows a choice of using the HDVD800's "Internal clock" or its "S/PDIF clock". These choices made available through the USB interface are referred to NOWHERE in the manual or its specs. Since I'm not completely familiar with details of S/PDIF applications, this leaves me in an uninformed position for the use of my product. By the way, an "internal clock" to the DAC would seem to obviously be associated with non-recovered clock type use which might explain why when I turn on BitPerfect, it locks that selection to "Internal Clock".
Although this seems to be a really nice sounding rig (I'm using it with a Beyerdynamic T1 re-terminated to balanced XLR-4), there do seem to be some suspicious implementations that makes Sennheiser's reluctance to release information rather credible (i.e., get everyone to hear what it sounds like in it's most common operating mode first and sell on that before they discover that all of those inputs on the rear panel may not really give them what they might presume)
If I'm out in left field with these presumptions, then someone please let me know
- Jeff