It also has the yamaha XG/XS midi engine right, I have a few similar hardware synths like yamaha qy100/nsx-39 (hatsune miku) that has these same dsp effects I believe. I write everything in trackers, for c64, gameboy, amiga, megadrive/genesis,psp they all have native trackers or cross platform tools (you can use furnace/deflemask and use simple tools to convert song to bin file for megadrive for example), the chiptune scene mostly uses these.
Seeing chips like the saturn (interesting chip) that has zero music tools to the power that the AICA chip has. until your project, seemingly untouched.
Yeah it would be possible it seems could have a native tracker on the dreamcast. Imagine your inputting notes into the tracker via the official keyboard and mouse, the tracker supports mod or xm commands but extends to harness the dsp and midi engine also. using instruments from both the aica midi engine and samples selected from folder. Testing some notes live playing on the keyboard before inputting. Thats the sort of thing I dream of.
I see it has some official but rare midi input hardware also. Things like c64/amiga, nes, snes, megadrive, gameboy you can hook a midi keyboard or sequencer to in a similar way.
Of course we are used to working with limitations with whatever tools even remotely work. Having your player read xm files from a folder would be enough to make it viable.
commands I used in my track were 0 (arp) , 4 (vibrato), 2 (porta down), EC (note cut), E9(retrig), 3(porta to note) and volume column commands like volume number and -(reduce by amount)
Thanks again for your thoughts. You can find me at avrilcadabra on youtube and such, love using consoles and old computers for music.