Just taking a moment to show off my completed build..
I chose to outfit my board with the Atarimax 32-in-1 Warp OS module for speed and 800 compatibility, as well as a POKEYmax for stereo sound. Both upgrades were greatly simplified by santosp including so many thoughtfully labelled breakout points. Audio out is available on both the enhanced 8-pin monitor port and a 3.5mm phone jack.
Yes, that is a light-grey Lego 2x4 tile used to block off the RF and channel-select switch holes, and to provide a mounting surface for the stereo phone jack.
All wrapped up in a very clean case and keyboard I set aside for this project. Finishing touch is an 'XE-touch' keyboard upgrade from Best Electronics. Anyone who hasn't experienced this yet, it is an absolute revelation.
Unfortunately, I did not know that POKEYmax and TransKey II don't get along with each other, so for now the PS2 keyboard jack is useless. I have searched the forums for a solution to this but have not found one.
Thank you, @santosp for creating this board! I have now been able to build the 'perfect-for-me' 130XE I've always wanted.
Shout-out to @Stephen for programming the TK2 PIC for me. Works great with a genuine POKEY. Hopefully I can get POKEYmax to cooperate.