Modding the PS Audio Directstream DAC MK1 and MK2

This DAC upgrade is insanely good. I initially let it burn-in  non-stop via the USB stick on the PST, for 200 hrs, but the sound has continued to improve under normal use.

The soundstage is rock solid with vocals and instruments clearly defined and focused.  The soundstage has also expanded in all directions, creating more separation and air around the performers. And the bass, OMG the bass, is crazy good. Tight, punchy, and incredibly rhythmic. 

This is a component level upgrade, without the price tag. 

If you haven’t heard 4400 with a GOOD power supply unit (PSU), then you haven’t heard their full potential.

With GOOD PSU (not cheap Chinese stuff), the sound improvement from 4400 without PSU -> to -> 4400 with PSU was much bigger than 4400 w/PSU -> APS transformers w/PSU AND VOCM MOD.

I can’t say anything about sound improvements when 4400 swapped with APS WITHOUT PSU mod

The XS4400 is not even in the same league as the custom designed nickel transformers.  Some of the "cheap" power supplies are designed better than some the the over priced supplies.  We know because we measure, test and sometimes modify them.

Our experience is just the opposite as with the nickel transformers the external supply makes little difference if any.

I didn't say there's no difference. There is. It's just my experience: power supply mod brought more changes than swapping 4400 with APS even WITH Vocm mod. 

The most of the things people described as APS transformers change in the sound: tight and beefy low end, melodic mids, and nimble highs - all these changes did my power supply mod after I installed the 4400 transformers. And APS transformers just tightened and cleaned up the same ALMOST perfect sound signature that I had with 4400 w/PSU before. Now, with APS transformers, it's perfect. 

Shame on me, I haven't done the Vocm mod before I swapped the 4400 with APS transformers... I  wish I could discern the Vcom mod impact on the sound.