When I put the D90 MQA into DAC mode I hear clipping distortion from my amp (Lake People RS-02), even with the amp pre-gain set to -12dB. I have to run the D90 in PRE mode and reduce the output by at least 7 or 8 dB to clean up the sound, plus the reduced pre-gain on the amp, but it still doesn't sound altogether clean.
I tried running the D90's RCA outs into my JDS Labs O2 amp, and that sounded clean. And the RS-02 sounds clean with other sources. Also the D90's RCA outs sound reasonably clean into my Loxjie P20, though the XLR outs sound cleaner. What might cause an incompatibility between the D90 and the RS-02 amp in particular?
And here's something else weird: I tried inserting a passive preamp (QED MA-34) between the D90's RCA outs and the RS-02 amplifier, to see if I could attenuate the signal with a passive volume knob there. But as I turned down the knob there, the audible distortion instantly increased and the sound broke up like it was going through a bitcrusher effect until there was just garbled noise left. What could be going on here? Could it be some kind of impedance mismatch? The RS-02 lists its input impedance as 10kohms.