Hello,
Inspired by the other posts in this thread and elsewhere, I decided to try modifying my own ATH-AD900x's. I registered on head-fi.org just so that I could post this message.
I wanted to use dual entry. At first, I drilled a hole on the right-side frame, analogous to the existing hole on the left-side frame. However, I wasn't satisfied with the job I had done, and so I ended up buying a replacement left-side shell from the Audio-Technica parts department and using it on the right side.
Also, I wanted to use A2DC jacks since these are Audio-Technica headphones. I found some A2DC jacks with cylindrical aluminum shells on AliExpress. They look like they're designed to go on the end of cables, though I don't know what the intended use for these is as usually it's the plug rather than the jack that goes on the end of cables. Then I had to figure out how to mount these. Borrowing the idea that the author of post #31 in this thread had gotten from watching the video referenced in that post — specifically the idea of using the "chromed" plastic part to hold the jack — I spent many, many hours over many days thinking of different ways I might mount these jacks in this plastic part. After a few failed ideas, I came up with the idea of cutting threads in the cylindrical shells of the jacks and using nuts with the appropriate threads to hold the shells in place. I had to drill a hole in the U-shaped notch so that the cylindrical shell would fit through. Here's what it looks like:
IMG_6794.jpg.
I had to grind some of the plastic pieces that the chromed plastic pieces screw into so that the jacks and one of the nuts that holds them in place would fit. Here's what one of these parts looks like after grinding some plastic away using a rotary tool:
IMG_6795.jpg.
Here's what it looks like when I put together the two pieces pictured previously:
IMG_6796.jpg.
Here's what it looks like when I reassemble the headphones:
IMG_6797.jpg. I used some grommets from McMaster-Carr to reduce the inner-diameter of the entry holes so that the A2DC plugs wouldn't be loose in them.
Finally, here's what it looks like with the A2DC plugs plugged in:
IMG_6798.jpg.
I spent a tremendous amount of time on this project, mostly ruminating about how I might mount the A2DC jacks and investigating various random hardware parts that I thought I might be able to repurpose for this project. Also, I spent a lot of money — easily worth more than the headphones cost new — on buying the various hardware parts (plus shipping, which often cost more than the parts) and also some tools that I didn't already have. In the end, though, I'm happy with how this project turned out. Beyond the enjoyment of using the headphones (now with a balanced cable, if I want), the "hack value" of the project was just as enjoyable.
