Sobered up (a bit) and time for another play with the DAC/Volumio settings.
Checking back I see that I only got the Chameleon DAC last November, but it feels like I've had it for years. It has a warm, inviting sound and can kick serious ass when required.
However it has several limitations: No DSD, no 32bit, no 192KHz, very restricted input options (coax, Toslink, USB and that's it) and blinding, industrial-strength LED's. Also the technology used is positively stone-age. The TDA1543 chips (all 16 of them) date from 1989 and the Tenor TE7022L USB processor can also be regarded as vintage.
But the thing just sounds so good! There is a big sprinkling of fairy-dust inside that simple, utilitarian casing.
Right, back on track, so the TeraDak V4.5 Chameleon has been optimised to run on its USB input, this automatically overrides the SPDIF connection and uses the separate Tenor chip to organise the incoming USB data into the I2S format for the DAC chips.
In-between is the upsampling board that converts all incoming data to 24bit blocks and a sampling speed of 96KHz. The TeraDak engineers found that they could maximise the audio quality of the venerable TDA1543 by running it at its flat-out-max of 24bit / 96KHz.
This upsampling board has been intentionally designed to be removable as that may further improve the SQ. So my software fix in Volumio effectively achieves the same, bypassing this board by doing the upsampling beforehand.
And it works! The overall feel is smoother, deeper. The removal of a hint of brittleness. Fine detail in the soundstage is clearer, bass is more defined, solid.
This won't work for every DAC but it might be interesting to play around with upsampling settings to see if there is a 'sweet spot' where a specific unit can perform at its best.
Enough for now, my brain hurts.