I've used the Firestone Cute Beyond amp without supplier for a couple of months and I finally decided to order the Supplier earlier this week, even though I had a feeling it would be tantamount to throwing money out the window (around $150 from the, I believe, only Danish store with Firestone products. Only $80 less than the amp itself).
Well, I obviously spent the first few hours after the Supplier arrived doing A-B testing, and with a fairly wide range of music, it was pretty much impossible for me to hear any difference with the Supplier replacing the basic 24V adapter that came with the Cute Beyond.
But then again, I've also been struggling greatly to notice any differences when I've been comparing 320 kbit MP3s (or 256 and arguably even 192 kbit) to the original CD tracks - so I'm guessing I just don't have a very good ear for details (although with regards to MP3 vs. CD I guess it's possible that the DAC in my Playstation 3 is less than great. Though right now I can't really say I'm feeling inclined to take a chance on a DAC as well