Well, we did it! The software from the Tandy Orchestra90cc cartridge is now running on the Dragon 64 without any additional hardware - here's a video of it in action: https://www.youtube.com/watch?v=LBWB0v4Ez3k
(possibly not the most action filled video on Youtube!).
Huge thanks to Pere (pser1) and Stew (sorchard) who did the clever stuff with disassembly, converting it to use the internal 6bit DAC and integrating my code to remap the keyboard matrix. So we can now play the huge archive of 2,000 odd orchestra files Pere converted in the previous thread. Hopefully Pere will post the latest ROM images here shortly.