Fair enough.
I'm not making excuses for 64.
I suppose the fact that the A12 is known to have some bass emphasis may, in itself, lead to a perception that there is (relatively) less midband presence and less treble presence, and thus a subjective impression, to some listeners, that perhaps there might be a slight veiling to the sound character.
Regarding the Calyx-M, though, that is known to struggle to correctly drive some impedances, isn't it? I recall they even had to introduce an in-line impedance adapter, didn't they?
I'd try with an iBasso DAP, as they're generally quite low output-impedance