I just did this mod, but i used a Toshiba TX179L instead because i like the self-closing cover.
I was able to get the TC9231N from ebay. An SN74HCT04N (Texas Instrument) from mouser.
I did order the board from OSHPARK, thank you very much. I did hower ever cheap out and solder the capacitor and leads directly to the legs of the optical out port.
I mounted the complete assembly on the gd-rom plate and the optical out is right next to the power supply port. I did not want to move or mod my gd-rom.
Because of the placement of the optical out port, i had to remove some of the material that separates the power supply from the rest of the dreamcast.
I did not get power from the legs of the oem dac, instead i got power from the solder joints on the back of the power supply. I used 22awg magnet wire. I also had some C0G grade ceramic capacitors laying around from another project. So i used those.
Pics in the next post.