D90 MQA is still being shipped on its way.
The behavior I described is with SMSL M500. But I just switch over to Topping D70s, I can't no longer adjust volume from my phone. Now I understand you dilemma. I don't know what makes the difference between SMSL M500 and D70s.
Yes, I can adjust volume from BOTH of my phone and the DAC. I don't have DSDs (except some samples), but play lots of MQAs. Volume adjustment from my phone doesn't break the hardware MQA decoding on DAC. Hope it helps.
Not sure if I missed something, but I connect my Raspberry Pi Roon Bridge to my DAC/Amp, and can easily change the volume from my iPhone Roon Remote app. I use device volume instead of fixed volume though, and I can fix my DAC at certain level, and change the output volume from my phone.
Amirm and Crinacle are among my few credible resources when coming to head-fi gear reviews. Way too many reviewers have their own agenda when doing reviews.