I have no issue monitoring the signal of my guitar and the signal coming from the computer without any DAW opened on my MacBook. I can control the level of the audio signal that is coming from the Mac using the DAW volume parameter on the USB audio page on the Profiler. In order to work without a DAW I have assigned the Profiler to be the input and output in Audio settings of the Macbook system settings. The direct monitoring option in the Profiler is active to provide latency-free monitoring.
I literally did the same thing, nothing is happening, And I jus did again, disconnected everything but the USB to the Mac, and Mac connected to an HDMI TV
I assigned Profiler as input /output, and in another instance I assigned profiler as input and HDMI/Macbook Speakers as output: nothing.
Both computer I used without an interface. No sound, until I kick in loopback or DAW.
Direct monitoring is on. and I used the DAW volume too, doesn't seem to be doing anything, I can't hear it, and I see the signal is still there, but volume is unchanged regardless of setting. When I open Logic, I get the Kemper sound output thru logic monitoring, but DAW volume does nothing. only control I have over sound is the Rig volume. Recording and everything is working fine, even splitting into DI/Master Mono works fine.
But I am confused where you say it works for you, but at the same time you are saying "OSX is unable to forward the incoming sound from an external audio interface to its own headphones or internal speakers without a loopback app or a DAW."
If you mean only Kemper as the external interface? then how is it working for you WITHOUT a DAW? are you using LoopBack??