The information on modifications on the PC Enterprises website was never saved by the web archive, so looking there is out. I remember in their printed catalogs they sold a mod kit for making the PCjr audio Tandy 1000 compatible, but I didn't buy it for my two PCjr's. I found the info elsewhere for the Tandy 1000 video mod and scrounged the chips from dead PC parts.
All the Tandy 1000 games I tried would work with 16 color video and PC Speaker sound - except for one that didn't allow selecting video and audio separately. So it wouldn't run in 16 colors because it couldn't detect Tandy audio.
Attempting to select Tandy audio on any of the other games would also fail.
I've searched off and on for years looking for how to do the Tandy 1000 audio mod but have never found the information.