Hey there, what makes you think the AY-3 cannot be sequenced? I don't see any reason why it cannot. As per the very brief specs, it can be controlled via MIDI CC messages, so I don't see any reason why it cannot be sequenced using an external sequencer or DAW. I agree, how in depth it can be controlled is not forthcoming in it's specs, but in terms of it being sequenced, it has MIDI, it accepts being controlled via CC messages, so it should be able to be sequenced.
The manual also shows some of the MIDI control: http://cdns3.gear4music.com/media/22/228605/download_228605.pdf
Also, I bought one of these about 2 months ago, I am still in flux after a house move, so my little studio is still in boxes, however it looks a cool little YM sound module, more limiting than the AY-3, but pure YM:https://catskullelectronics.com/YM2149
This is the one that Farvardin mentions in this thread, which the guy at Catskull used to build his version:
Atari Falcon 14mb, 68882, Dual 8gb CF & Steinberg FDI
Atari Jaguar, Rotary controller, Skunkboard & Cat Box
Atari 520STFM 4mb, TOS 2.06 switcher, OverScan, GigaFile, PARCP-USB, Unicorn-USB, System Solutions MiniS HD, SyQuest drives, ICD Link II, PhatBoy MIDI Controller, Philip Rees 5M MIDI merge box, Soundpool M04, Steinberg MIDEX, SMP II, Emagic Log 3, C-Lab Unitor 2, Combiner & Export expanders