Well, it took a bit longer to finally find the time to get around to this project, but over this past weekend I finally made the commitment. Took at least 3 hours to get everything done, since there are a three distinct tasks. On the theory that a picture's worth 1000 words, and my experience may help others, I'm going to provide photos here.
First, just one editorial post-mortem comment regarding the plastic clips provided for use in attaching the HT cable to my headphone (HP) cable. Smyth provided five different size clips (let's name them #1 - #5 in order of increasing size). The first three are smallish and "circular", clearly intended for a particular roundish shaped HP cable. The last two (#4 and #5) are flat and clearly intended to attach to a flat ribbon HP cable, with #4 being smaller. The clips are closed to start with, but one end opens slightly producing a U-shape which can then wrap around the HT cable (pushed into the closed U-end of the clip) and you can then push the open part of the clip onto an edge of the flat ribbon cable.
The HP cable for my Stax SR-009 is of the flat ribbon type and is about 2.5m long, with 6 individual strands of wire running through most of the primary cable. The six strands then split into a Y, with two 3-wire smaller flat ribbon cables attaching to each transducer. In addition, I have a second Stax "extension cable" which adds another 2.5m to the overall cable length from the headphones to the amp. Total length is about 16ft so I used all 10 of the largest #5 clips provided, spaced evenly throughout the full 16ft cable length, as the primary method of securing the A16's HT cable to my HP cable.
In addition, I used all 10 of the somewhat smaller #4 clips for special needs along the 16ft HP cable length. I used three of these #4 clips to secure the HT cable as it ran down the front-facing edge of the plastic HP band of the SR-009 from its 2.5mm 90-degree cable connection to the head tracker (HT) itself, and then down past the R transducer. I used two more of these #4 clips to secure the HT cable to the thinner 3-wire flat ribbon cable running from the R transducer to the Y-junction where it merged with the 3-wire cable running from the L transducer, to now form the main 6-wire primary cable. Total of five #4 clips used here.
I used two more of these #4 clips immediately on either side of each of the two "extension" cable junctions to provide additional "cable tie" neatness, one for the Stax flat ribbon cable connecting to the Stax extension cable, and the other for the primary Smyth HT cable connecting to the HT extension cable (since I needed more length to reach the A16 than the primary HT cable provided). So four more #4 clips used here.
Finally, I used the one remaining #4 clip to "tie down" the HT extension cable where the Stax extension cable plug inserts into the Stax amp. I then ran the remaining length of the HT extension cable under the Stax amp and behind my equipment rack, coming up out front again under the A16 on the shelf below the Stax amp, so that the 2.5mm plug could insert into the A16's front HT socket for UserA. I tied up the excess length of the HT extension cable behind the rack for neatness, with a twistie.
My editorial post-mortem comment about the clips (specifically the #4 clips) is that they seem to lose their "spring-back memory" quite quickly, spread as they needed to be to press onto the my Stax cable and Stax HP plastic band as I used them. Perhaps they would retain their shape and tension better if they had to spread less. Bottom line: I'm not sure these are going to hold very well. As unattractive as it might be, I might have to use "painter's tape" to wrap fully around the points along the Stax flat ribbon cable where I've used those ten #4 and ten #5 Smyth clips to hold the HT cable, in order to securely keep the HT cable from coming loose. We'll see how well these clips hold up in normal use by themselves, but I suspect I may need to supplement them each with a piece of fully wrapped painter's tape (so as not to do damage to the cables from adhesive).
Now for the pictures of the results. Really came out great. I'd been using my A8 at this location forever without a HT, simply because of the physical situation and that I didn't want to go through the trouble I went through this weekend to install the optical ST unit. But now that I've finally done it, I'm really pleased (ever since experiencing the HT back at CanJam SoCal in 2018).
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Part one of the project involved placing the ST unit on top of my wall-mounted bedroom 65" Panny TV using a strip of 2-sided tape. I also had to run the 3.5mm ST cable connected to the ST unit down behind the TV through cable guides, and out through a hole in the wall (in the middle of the wall mount) running into the open equipment space behind the wall where the TV is mounted. This is an old space (opposite my bed) where I used to have a very heavy 35" CRT TV built into the wall (sitting on a very strong shelf). Under the shelf is space (covered by a black speaker grill, as you can see in the pictures) for two audio speakers which are fed by my Yamaha AVR (in 2-speaker stereo "party mode"). As you can also see from the pictures below, there are even two cutouts above the TV for two VCR's (DVHS and ED-beta) which are no longer in use. The ST cable then ran (along with a number of other cables) out through an exit hole on the side outer wall of the equipment space, and over to the back of the equipment rack where it could connect to the ST input socket on the rear of the A16. Fortunately the total run length was under 15 feet so I didn't need to use the ST extension cable.
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Part 2 of the project involved attaching the HT clip to the plastic headband of my Stax SR-009. After figuring out which way was going to be "up" for the clip I attached the piece of black sponge (with 1-sided adhesive) provided by Smyth to the bottom of the clip. This prevents cosmetic damage to the plastic headband when the clip is attached using a rubber band.
I used the largest of the three rubber bands provided by Smyth, which turns out to be the absolutely perfect length to secure the HT clip to the plastic headband of my SR-009.
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And finally, part 3 involved attaching the HT cable (and HT extension cable) to the side edge of the Stax HP cable (and Stax extension HP cable) securely, so that this second cable would not simply dangle off of my ears and HP and get tangled up on its 15 foot run to the amp/A16 equipment area. Furthermore, it initially had to be neatly guided and secured out of the 2.5mm connector on the side of the HT now clipped onto the top of my HP band, down the edge of the plastic headphone band and down the 3-wire ribbon cable out of the R transducer on my SR-009.
And then the HT cable and extension cable had to make its way across my bedroom, to the equipment rack area where it could cleanly plug into the front HT socket of the A16 without just dangling off the front and onto the floor. It all had to be neat and "hidden" from view as a distinct second cable as best as possible given that it actually IS a distinct second cable now running out of my headphones.
Turned out pretty decent.
And yes, that is a dbx 14/10 computerized equalizer, circa 1987. I use it for "analog tone control" for the two speakers under the TV, for when I just want to hear sound through speakers instead of doing "serious listening" via headphones and SVS.
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Now to actually experience HT effect in my bedroom location. Haven't had this here since 2009. Finally.