I’ve found your previous post about the Tascam: https://forum.audacityteam.org/t/only-2-channels-will-record/24506/1
Looking through that I don’t see if you tried using the Tascam Control Panel to set the output of all 4 input channels to outputs 1 and 2.
If you have not tried that, please do (see page 19 in the Tascam manual)