Below is a close up of the Class-D amplifier section, which uses the TPA3116D2  50W x 2 (Stereo) amplifier IC.  The heatsink and heatsink compound has been cleaned off to show the pinout and associated components.

(https://www.ti.com/product/TPA3116D2)

I've been looking at the input audio signals on my scope, and I'm starting to get suspicious that the input gain range is too low, which would explain why the volume doesn't get very loud.   Normally a 2x50W system at full volume can get really loud.  This thing at full volume almost sounds like a 2x20W radio.

I'll probably at some point post up a partial schematic of the DSP, OpAmps, to TPA3116 connectivity, to show how the DSP outputs through the op-amps and out to AMP.....