I just got my old bbc micro setup so to build this crazy project i always wanted to do. Out of leftfield this idea hit me which i thought would be perfect for you:
THEORETICAL 8BIT SAMPLES ON A SINGLE DMG
Sync Pulse channels 1 and 2 inversely without any gaps inbetween and mix to create a single constant voltage then control volume and mix with the wav channel. Create some crazy methods to interface this alltogether, wallah 8 glorious bits for sample playback.