The problem is with the midi i/o. The usb interface has ports for midi in/out. MTS playback
operates normally with no errors, my USB interface says it's sending midi out, my synth
apparently receives it, but reports "midi buffer full" and "midi communication error".
Maybe there's a MIDI loop. Does MIDI playback work if you unplug the MIDI cable that goes in the USB device's In connector?
Initially, MTS reported a problem with my "mixer" when I tried to record using the new
interface. It recommended using the control panel to add hardware - this message was
generated when I clicked the MTS Input button.
Windows showed that message. Most likely your USB device doesn't provide any volume controls, and hence there's no mixer window.