So, it turns out I must install dspMixFx_UR44 to mute the inputs (or unmute) as needed for input monitoring. Although I can download bundled software that includes dspMixFx_UR44 (and it runs fine) - I’d like to find a way (a link or a hack) that excludes anything else but the dspMixFx_UR44 that I need. Specifically, I don’t want eLicenser on my machine (2015 MacBook Pro) and I don’t want any sound libraries. I just need dspMixFx_UR44 and the USB driver for Mac.
I got dspMixFx_UR44 bundled with Tools For UR44 here: