since OS version 1.60, MC-707 works with USB driver mode set to Generic.
USB Midi Controllers
hitachii
#255
The Elektron Digitakt and all of its features works magnificently with the Axo via USB and Din. The Novation Launchkey Mini MkIII also works without issue (including the Launchkey's built-in arpeggiator!).
Have been running midi via the UART pins and no resistors without issue. Mentioning that because it was sort of unclear whether they were required for UART in the same way that they are for using the pins behind the Din connector. Though, I'm not TX from the Axoloti so maybe things will change and will require the resistors and octocoupler when I do?
ivofx
#256
That controller looks really cool, could not find it on eBay or Amazon however. You lucky 
https://www.soundonsound.com/reviews/cme-bitstream-3x
Interestingly, when following the URL written on the unit, we see a sort of portfolio of devices that the creator worked on which includes the Teenage Engineering OP-1:
chaocrator
#257
yes, Bitstream 3x not easy to find hese days, it was discontinued long time ago.
used to be my dream controller around 2005–2006, so finally i got it.
nicotep
#259
(not strictly a USB Midi controller but) Op-z is working fine both as a controller and a sequencer, sending clock too, directly from the USB. No need of the $$$ Oplab 
floodcomics
#260
Korg SQ64 will not work via USB, regardless of Axo power source (USB or PSU, tested @ 7, 9 and 12V)
hitachii
#261
Interesting. Are you using USB MIDI or with the TRS cable? Not sure if the SQ64 does or doesn't send MIDI over USB, but Axoloti recognizes my Minilogue xd through USB. It should recognize the TRS MIDI by default.
If you're trying with a MIDI Din to TRS adapter and it's not working, did you by chance order it off of Amazon? I bought one for another reason and I hadn't seen the reviews that it was falsely advertised. It was 5 pin DIN, but was wired for old testing equipment or something.
floodcomics
#262
The SQ64 does do USB MIDI, but the Axoloti can't deliver sufficient power to run the SQ64 via USB. TRS MIDI (type A) works without issues.
Maybe you got a type B cable - it's not such a difficult soldering job to convert from A to B though: