Well here I go again :)
Had my PC360s from Amazon for a couple of days now (along with the ASUS Xonar U3), my impressions:
Seems like a better set of cans than the PX5, for sure. But then again with the phones being $170 and a mixamp another $130 on top of that, you'd hope they were. What I'm getting at though is it seems like these are expensive, but justified cost whereas the PX5 had a high-end feature list but not necessarily high end performance. The build quality is a lot more solid, and they are definitely lighter (but lighter by design, since there are no electronics/batteries in the headphones). They are comfortable, but I do get some pain/discomfort after wearing them for too long. I think it is that they squeeze my head too much. I don't know if that will loosen up over time or not. If it does not improve, I may actually have to return them. I can't go for more than a couple of hours without getting a headache.
As I suspected, the cord on this thing is ridiculously long. If I end up keeping these phones I will have to cut them and solder in an inline connector so I can have a short run for mixamp use, and a long run for PC use. I can find 4-pole 3.5mm male plugs on eBay, finding 4-pole 3.5mm female plugs seems more difficult.
Didn't try the mic much, but one thing I don't like about it is it seems to be quite long, and stretches way in front of your mouth. That's great for picking up sound but also it picks up my breathing too. I will have to try more placement options but also the mic only "flexes" in one axis, so placement options are also limited.
The volume control is very handy, especially using it on the PC since the Xonar U3 does not have a hardware volume controller (unlike the Xonar U1 which IIRC is the same hardware in a different package). One thing I didn't expect was that the volume control has a limited range. You cannot totally mute the sound using the on-headset volume control, only lower it. So far it seems I have enough volume modulation that it's not a big issue, but would have been nice to have full mute-ability (mutability? :)) using the on-headset volume control.
The volume control also comes in handy when using the U3 on my mac, which was a pleasant surprise since the box does not state any kind of mac compatibility. I plugged it in and saw that it was recognized as "USB Advanced Audio Device" in OSX. There are no drivers so no access to fancy features like DH, but it works. The headphone amp seems to be stuck in high gain mode though, since the sound is OUTRAGEOUSLY loud. I have to lower the system volume to as low as it goes without muting the sound (even below 1 square on the volume scale, using the sound prefpane or Audio MIDI Setup), turn the on-headset volume controller all the way down, and then turn the volume slider in iTunes down even more (to about half) before the volume is at my typical listening level. Then I can use the on-headset volume to modulate the volume a little as needed. But anyway it was kinda neat to see that the U3 worked on the mac, although ultimately I will be using the mixamp with the mac instead. I tried to find some of the old Xonar U1 drivers (again, same hardware different packaging so I think it might work) that ASUS used to have for OSX but it appears they have disappeared from the internet. However, it also seems like they won't be Lion compatible anyways so maybe it's a lost cause even if I could find the drivers.
Anyhow regarding the PC360 sound, I can only do limited testing since my Astro mixamp is not here. However, using the Xonar U3 on my PC allowed me to do some DH gaming, although my selection of PC games isn't super great for testing surround sound. What I heard seemed pretty good, but will save judgement until I get my mixamp in the mail so I can make a more direct comparison to the PX5s using some 360 games like Bioshock 2.
What testing I did though, seemed fine. The best example I could come up with on my PC was the FPS game Sanctum. In this game you build towers and mazes to slow down and stop waves of enemies from reaching the "core" and destroying it. Anyhow I set up some lightning towers which have a passive humming/crackling sound and standing next to one I was able to pinpoint where it was in relation to me. I closed my eyes, and jerked the mouse around to screw up my orientation, then I panned around to see if I could tell where the tower was in relation to my view. I could always locate it, and recenter it so that I was looking at the tower again with my eyes closed. I noticed that the weakest part of the soundstage seemed to be the very front. It seemed like the sounds quickly transitioned from being front+right to front+left as I panned across. I did not notice this as much if the sound was behind me, only in front. I will see how it goes with the mixamp (although I do not expect very different results, since it's still using the same DH processing).
Sound wise though, didn't you guys say these things were bass light? I honestly don't see that at all. Granted, my viewpoint is definitely biased somewhat since I own and like the sound signature of my Ety ER4Ps, but these things have more than enough bass for my tastes. In fact on the PC, I have created a custom equalizer to bring the bass down a little and emphasize the mids/highs. I can't imagine wanting a headphone with more bass. I'd definitely consider these to be "fun" phones borrowing from the original ratings on this thread. I'll be curious to see how I like them on the console, where I won't have the option of creating an EQ to compensate for the headset's natural sound response.
Anyway, they sound fine in the musical tests I ran. Could not really hear any distortion even in difficult passages, and the distortion I did hear I think I am beginning to attribute to bad mastering on behalf of the audio engineers. I hear the same distortion in the same places on several sets of headphones and playback systems, at that point I can only conclude that it is the source material. In fact some of the distortion I heard with the PX5 was probably the same.
Overall they seem like a solid set of headphones, however someone had to go and post that modmic link a few posts up :), now I'm thinking I might like that route better. I might be able to find a set of cans I can use more generally (both for music and gaming, making the expense more justifiable), with a sound signature I like better, and still have a good integrated mic solution using something like the modmic.