I have built a linear regulated power supply rated at 5v 4A and am using it to feed DC to the Boss DAC. The regulator used is the LT1083 LDO regulator. The sound has become significantly quieter resolved and clearer.
Any DAC will improve with a good PSU.
Glad that you like the Boss with the linear PSU. I am using the same on the second setup (first one is the Katana DAC)
I have also build linear power supply based on mdXS with LM317 regulator. In the first test i feed Rpi and DAC via RPI USB port fed by one regulator. Yes the sound was improved as you describe. Then i start to make second revision to put own supply for Allo BOSS. Disconnect(turn) RPI pins 2,4 to and connect power directly to HAT pins 1,15. I didn’t make any changes to BOSS board. For a some reason after these that sound level goes very low like there is volume control in position 10/100. I have to put volume in very high level on power amp(Yamaha AV-amp) to hear something. Same behavior will continue if i feed power via RPI.
Did i broke Allo Boss board?
Good reason to buy Katana when it comes available 
Do you hear the difference against ifi? Can you upload image of you linear power supply?
Yes, there is an improvement in sound quality. I don’t have any measurement tools, but the noise seems lower as there were no switching harmonics.
I am using a 2-stage linear PSU. The first stage has a 5A trafo feeding a bridge rectifier with 10000uf x 2 CRC filter and hf filter caps. The DC out then goes to a LDO LT1083 regulator, and then to the RPI and Boss.
I am sticking with a linear PSU now, instead of the switching adapters.
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