Different Garageband Sound Issue: with USB mixer & Moog devices

The following equipment and config was working fine, then quit without any changes to the system.

Configuration:

MacBook Air M1 2020, 8GB RAM, Sonoma 14.4.1

Garageband (have removed and reinstalled already per online recommendations):

10.4.11

Using either a Mackie Onyx BlackJack or a Pyle PMUX6 in order to connect either a Moog Etherwave Theremin, or a Moog Werkstatt analogue synth. to my Mac for G-band. Have tried routing with stereo or mono 1/4" cable, or with XLR.

I've tried with both Line in, stereo, and mono on either USB ifx (Pyle or Mackie) cables, and bought new/replaced all to be sure of no issues there (shielded, premium quality cables).

PROBLEM: Maybe a G-band bug? I've searched on all the "no audio in Garageband," and done all those tests/ruleouts.

I have to crank input volume on it until it's pinging to hear anything regardless recording level in Garageband. I have System settings open while working and can see in Sound Input with both the Theremin and Wekstatt are sending normal level audio (when I can't hear in Garageband) and pinged (when I can barely hear in Garageband, but it's distored and scratchy/static-y due to having to over-drive input levels just so G-band registers anything.

I'm able to run an Akai MPK Midi key board into G-band but sometimes it mutes as well in G-band. So then I open a separate sound app (like the Moog Model D app), strike the Akai key one time and all levels are normal again in G-band.

This is why it seems to be G-band: it does this with either the USB ifx from the analogue devices in, and with the Akain (but the latter is "fixed" when I open another app and play one key, as noted). There's just not another "app" for the Werkstatt and Theremin to confirm the level changes and comes back to normal the same way it does with the Akai midi. Nothing will make the USB ifx audio from Theremin or synth come through (and, again, both worked fine before ... possibly recent version of G-band is all I've changed.

I have had it working with either prior as noted.