I think I am one of the few people not impressed with iFi power supplies.
I have had better luck at a fraction of the cost using medical grade power supplies from Mouser (don't buy this type of thing on Amazon).
If a battery did not fix your issue, then the issue is the amp itself. Battery power, while "pure," usually leads to loss in dynamics since they have a very limited discharge rate. Any 'haze' or color in the upper ranges should be from the amp.
At the end of the day, what you listen to is the power supply colored by the transistors. If you give it "perfect" power and do not get "perfect" sound, then the issue is the circuitry. You can attempt to mitigate this by using different filters in the DAC to roll off the upper frequencies or even use parametric equalization.
I think in you case, the best thing is to accept the limits of what you have, spend the least to get rid of the worst issues, and enjoy the music.