Have you seen Serda Waveblaster module?
Maybe we can use it in same way as cheap but powerful soundcard for our little ATARI.
Pokey will be for effects and Waveblaster for music.

How it sounds?
https://www.youtube.com/watch?v=GWXRJGTMlkU

Interface? Via internal MIDI??? Here is Atari ST.
https://www.youtube.com/watch?v=P3fscX057gQ

XE/XL midi?
http://ixkuczek.republika.pl/ixkuczek.html

What you think???

Duke Nukem 3D
https://www.youtube.com/watch?v=rhDC0A9QsIE

MIDI tracker:
lowcost - RF1MidiTracker
http://www.rf1.net/software/mt
free - MIDItrk
https://github.com/localhost/MIDItrk

Serda
http://www.serdashop.com/waveblaster

Datasheet
http://serdaco.com/files/SAM2195.pdf

Tip for Toriman: SAMari???