Well, I am about to come full circle with my audio setup. I started with a pair of HD600's for quiet-time listening, and found they didn't pair well with my 80's vintage Carver receiver. This led me on a search for a more headphone friendly solution. I ended up with a Peachtree Nova, which I love thanks to it's built-in DAC and great analog and digital switching capabilities. I lived with this nice setup for a few months but I was never quite happy with the HD600's - they were so balanced I never found anything I liked better, but I was always bothered that they were a little on the bass light side of things for my preference. Then a month ago, I discovered the Denon AH-D7000 and everything changed. They sounded fantastic to me, but I started worrying that with their low impedance, they weren't a good match for the Nova (30 ohm output impedance). This is about the time I discovered the O2, so out of curiosity, I bought one and a Violectric V90 to see if a low output impedance amp would be a better match for the Denons (even though I couldn't detect any problems with the Nova, which sounded great). What I found is that all three amps sounded extremely similar to each other. I came to the conclusion that, because the Denons have very stable impedance across the audible frequency range, they are not picky about amplifier output impedance. With this conclusion on my mind, I decided to see how my Carver receiver sounds with the Denons. I hauled the Carver home from work today (I have been using it in my office system) and hooked it up. Well, what do you know? It sounds terrific with the Denons - I really can't tell it apart from the Nova or the O2. Maybe with extreme eye squinting and A/B switching I could spot some tiny differences, but my primary conclusion is that the Denons are just really amp friendly and I really don't need any special gear for them. The bonus for me with the Carver receiver is that it has Tone Controls. With all the other setups I've sampled and owned, there were always some albums that weren't mixed "neutrally" and sounded poor to me. Some old rock albums that sound thick and muddy or 80's CD's that sound too "U" shaped. For 80% of my collection, everything was great, but with that other 20%, there was nothing I could do so I just avoided listening to them. So I've come full circle - back to my beloved Carver. I'm going to keep the O2 because it's just really cool and I like it - I'm sure I'll find a use for it. I've already sold the Violectric because I don't need it, and now I think I'm going to sell the Peachtree Nova too - I'm going to Europe this summer so the extra money will be helpful. I will be in the market for an inexpensive DAC to replace the Nova's DAC, but even if I spend $300 or $400, I'll still come out ahead. Sorry if this wasn't interesting to you, but I had to let it out somewhere. I thought this was a good place because it was NwAvGuy's blog that educated me about output impedance and the O2 which got me to experimenting. Thanks for reading!