1) I have two MIDI recording devices specified in the MIDI device manager:
a) "MIDI input system device" -> "16:32 Audigy MPU-401 #2 (duplex)"
b) "QMidiRoute" -> "132:1 qmidiroute: out 1 (read)"
2) On each MIDI track under "Recording filters" I can select the following devices:
b) MIDI input system device
3) No matter which device/channel I select, I only hear input from "MIDI input system device" when "MIDI Thru Routing" is enabled, although it does record from the correct source. However, this is very unhelpful in actual usage scenarios where I have multiple keyboards each on their own MIDI device or channel that need to be recorded simultaneously. Not being able to hear the input filters through the MIDI Thru is like working blind (or deaf?).