I had some time last evening to do a few simple non-scientific tests. Played Moanin’ by Art Blakey, an album I love and listen to quite frequently and tend to know quite well. I played the MQA version on the same Topping D90 DAC but simultaneously on the MQA (USB input) and non MQA one (COAX). Both were “zoned” in Roon and I kept switching between both a number of times during the tracks or leaving a track to play fully via USB then playing it again via COAX.
Bottomline: I can’t hear a difference between the MQA and the non MQA input (in other words a full MQA unfold or just the first unfold done via Roon). Ultimately, switched back to my RME ADI-2 DAC and a MQA song unfolded by Roon only sounds better than a full unfold via the USB in Topping.
Just for the sake of completeness, gear is Allo DigiOne Signature to the COAX input of the Topping D90 MQA DAC and the MQA is fed via USB directly from the RPI, Rega Elicit R amp and KEF R3 speakers. The PS for the RPI4 is a linear Swagman Lab
The Topping is a decent DAC, no question, but the RME is simply in a very different league.
For me personally, the insight is that looking for a better DAC is the better purchasing strategy rather than looking for an MQA DAC.