I have my Boutique TB-03 connected to my MX-1 on USB port3, which means a single USB cable for Power, MIDI and audio.
One needs to be careful though, as USB3 is the only powered USB port. Which means: Connecting a Boutique to a non-powered USB port is tricky, as the Boutique expects power from USB once it get´s connected via USB. It seems there is an Arturia USB Y-cable that does the trick to connect Boutique to USB1,2 or 4, but I haven´t done that myself.
On the other hand: I also have a TR-8 which I did not connect directly to the MX-1 (since the USB transmits only main out, no single outs to MX-1 via USB). So the TR-8 is hooked directly to the computer, which means I can route all channels incl. single outs to Ableton tracks/channels, which then get routed to the MX-1 outputs.
End of story:
MX1-1 = BD
MX1-2 = SD
MX1-3 = Claps
MX1-4 = Rim
MX1-56 = Toms
MX1-digi = HH + Cym
MX1-USB1 = System-1
MX1-USB2 = currently unused
MX1-USB3 = Tb-03
Works for me :)
Plus, using Ableton as an in-between, you can freely assign channels, so you could move the toms to the mono channels 1-4 if that´s what you would like to have. Or you could move the USB3 input to USB1 output in Ableton, if that layout is what rocks your boat. It can get complex, but that´s the price for being flexible.
Caveat: In order to have Ableton use TWO interfaces, you need to combine them via ASIO4ALL or a corresponding utility under Mac (but I don´t have one).