Can't believe I haven't joined in on this thread yet! I've been using the AP1+PP combo for several months now, and it's become an indispensable part of my system. Obscenely clean sounding - simply the best I've heard in terms of transport. For some history, I've owned quite a few CD players and transports that cost me a lot of money.... far too much in retrospect. My favorite was probably the Marantz SA-1 with Audiomod upgrades, which was roughly $14k all told. The Audiophilleo AP1 with PurePower, driven by any laptop (nothing fancy required), is a far better transport than the Marantz. Same thing applies to my old transports from Esoteric, Krell, Lexicon, and various others. As many of us are gravitating towards computer based playback rather than fiddling with optical discs, a device of such high caliber is highly welcome. I know some guys spend big bucks on the MacBook Pro with the idea that it will sound better as a USB playback device. I say: of course, if you like Mac then go for it. But if SQ is your chief concern, you'd probably be better off going with any decent laptop, and getting the Audiophilleo gear instead. A nice Windows-based machine plus an AP1+PP is roughly the same price as some of the MacBook Pro options anyway.
Here's a scenario some people might be interested in - what if you already have a really good USB signal to work with? Well, in those cases, the AP1+PP may have less of an impact, but in a really high end system it's still worthwhile in my opinion. For example: I use an Auraliti PK90 music server. It's basically a dedicated computer running Voyage MPD Linux, custom tailored for audio duty. It uses the SOtM tX-USB card which is tightly regulated and produces one of the cleanest USB signals around. It doesn't draw power from the motherboard but rather gets it straight from the power supply via 4-pin connection. In my case, I feed it with a NuForce LPS-1 linear power supply. So basically this is an ultra-clean setup dedicated purely to USB playback. And in that sense it's excellent, among the best I've experienced (up there with the SOtM sMS-1000 which costs a lot more).
But you know what? Adding the AP1+PP still makes this already clean signal sound even better. How? I don't really know or care. It just does. I noticed it sounding better right from the start but didn't fully appreciate the difference until I went back and used the system without it. It's a significant improvement over what I thought was the best signal around. That's quite a feat.
I'll have more to say about the AP1+PP when I find time for a full write up. But for now I can say it's an absolute reference grade option. I recently had a chance to hear the new Bel Canto RefLink as well as the Empirical Off-Ramp 5. Both of those are quite good in their own right, and both bring a few things to the table that might be appealing for certain users (HDMI, AES/EBU, etc). And I know we tend to love newer stuff and figure it must be better than the older.... but in this case I just didn't hear it that way. Neither seemed, to my ears anyway, to match Audiophilleo combo in terms of resolution as well as pure involvement. The AP1+PP just seemed more lifelike to me, and this was on a highly transparent speaker based system where the differences were more noticeable than usual. So At the end of the day I'm sticking with the AP setup.
