Thanks guys! I'm still chewing on what options are best for me and available. Looks like ES3/5/6 are my preferred options presently as they could route into my existing interface options and by physically pretty easy to manage (vs. lots of re-patching in hidden corners of the studio). Yes making a more "networked" studio to bounce audio & CV around my various devices (like jb61264 going into Hydrasynth) would be great; makes me wonder how much I/O I will actually need!
I'll take a moment to bake into the thread some other helpful resources I've found on this question (in case anyone else refers back to this thread for info).
-- Sweetwater's list of DC-coupled interfaces: https://www.sweetwater.com/sweetcare/articles/which-audio-interfaces-are-dc-coupled/ ... lots of options including the MOTU devices mentioned above
-- Expert Sleeper's list of interface modules and expanders: https://www.expert-sleepers.co.uk/moduleoverview.html
-- other options (mentioned above and consolidated here): Ornament & Crime, ADDAC 222/221, Befaco VCMC & CV Thing. Many basic "gate to MIDI" options from Doepfer, Ladik, VPME
-- Loopop on Midi to CV and back:
-- Divkid on Midi to CV and back: