I recently acquired a UR44 and am getting familiar with the hardware and software. Included in the latter is an application called DSP Mix FX which allows the user to monitor an input and add effects, without using a DAW. Among the effects that I find in DSP Mix FX are the Yamaha Guitar Amp Classics. Cubase Elements includes VST Amp Rack, which sounds better to my ears than the GA Classics. Is it possible to use Amp Rack within the DSP Mix FX application somehow?

Afraid not- since the dspMixFx is not a VST host.

Thanks, I thought so. Is it the case that dspMixFx functionality can’t be enhanced with any add-ons?

I think thats the case, yes.