I would probably do the following:
A small midi to cv module = alm busy circuit mmmidi or befaco midi thing.
Get a compact multi function module = Mutable instruments stages.
A clock divider = don’t have any specific in mind.
And get a small headphone output = ALM HPO
Stages would be the main attraction here you can send trigs from octatrack via the midi module to fire of envelopes to patch to Atlantis and also send LFO’s or random voltages.
If you want you can send the audio directly into the Octatrack (it can handle it) without the use of a euro to line conversion, so the HPO would be more for on the couch patching without the Octatrack.