I just picked them up today. Initial impressions are a little mixed, but favourable.
The don't quite have the amazing levels of isolation I was hoping for (I think I was being a little unfair in my expectations) - the noise from my work computer is now incredibly low as to be almost non-existent, but my very noisy gaming PC can still be heard (it's a Core 2 Duo SLI machine that has a lot of fans in it), but at least the noise no longer irritating like it was before. Don't get me wrong, the isolation is still noticeably better than the PXC250, but you get a (false) impression that the active cancelling is not as good. This isn't true of course - the technology is exactly the same - its' just just that you get most of the isolation passively from the fully closed design and the active cancelling finishes the job off so to speak. I'd say subjectively it isolates about 6 dB better than the PXC250, so that is nothing to sneeze at, given the good job the PXC250 does.
Soundwise it strikes me as a hybrid amongst the PXC250 / HD555 and HD595. Tonally I guess it is closer to the HD595 than any other Sennhesier I have tried and it seems to share the HD595 characteristic of being "forward" sounding. But it does not have the treble grain that I noticed in the HD595. It's not as coloured as the HD555 either - it doesn't have quite as much of the boxiness and "mud" that I noticed in my previous HD555. Bass seems quite well defined, uncoloured and neither lacking nor excessive. Imaging does not seem to be a particularly strong point unfortunately - a fault that in my opinion the HD595 shares. Unlike the HD555, HD580 etc that can really provide near pin-point instrumental separation, accuracy and depth, these are a tad rough and vague in this respect. But I have noticed from experience that extended running in helps this situation considerably. Overall though, it has a very unfatiguing and smooth sound. Since sound is subjective anyway, I'll leave my sound impressions there.
I'm driving them perfectly well directly from the output jack of my X-Fi soundcard. Tried a CMoy with absolutely no benefit, so it seems that like the HD555 - this headphone is very amp friendly. The PXC350 has an inline volume control on the cable and this is actually extremely good for use with a computer - it makes volume changes quick and easy - so if you are driving them directly from a soundcard then you don't have to go fiddling with the Windows volume controls all the time.
I was surprised to find the cable on the PXC350 is detachable, but it also has a (very) proprietary connector, so I don't think it is a worthwhile candidate for re-cabling - either from the practical perspective of the proprietary connector nor from the perspective of it actually improving sound (I don't think the headphone is good enough to benefit significantly from a new cable, especially as the stock one is pretty short to begin with).
To the bad points - the phones are heavy. Each ear cup takes a AAA battery and you can really feel the weight compared to the HD555 and HD580. It's not too bad but it might be fatiguing if you were thinking of doing exercise with these on. I've been wearing them now for a few hours whilst working at my computer and whilst I can feel the weight if I tilt my head it's not uncomfortable. Infact they are incredibly comfortable - even better than the HD555, HD595 and HD580 on my head. It's just the weight factor if you go tilting your head around too much!
Like the HD555 / HD595 with their internal "deflectors", the PXC350 has an even more radical version of it - so much so that it can actually make contact with your ears. It's probably more radical then the HD555 implementation because it serves to cover the area in the ear cup that houses the battery. I'm surprised about this - I just wonder that if some people have some pointy bits on their external ear it might make contact with the deflector and possibly make wearing them uncomfortable. My ears don't have any significant sticky-out bits but I can feel that one bit of my ear is only a couple of mm away from the deflector. But at least the deflector is made of a reasonably soft, pliable plastic, so perhaps it is something that one could get used to if one's ear did make contact with it.
As far as active noise cancellation circuit hiss is concerned, it is much less than the PXC250, however I can't make a definitive judgement at the moment. Reason is that unfortunately my tinnitus has flared up very badly recently and by nature it is a type of hissing sound. So if these headphones do hiss, I wouldn't know it. But I do hear hiss in the PXC250 today that I am not hearing on the PXC350 today, so they are certainly far quieter - I just have no idea if they are deadly quiet or not and will probably not be able to tell unless I have a day where my tinnitus goes away.
Anyway, that's about it. A good buy I would say if you want a high degree of isolation from a continuous type of noise in a closed, full size design and aren't after true, audiophile calibre sound. I don't think it is worth the retail asking price of $599 here in Australia, but it is for sale from $400, which is more reasonable and realistic to me.
I'll close by saying that after 7 hours running in they have improved noticeably, particuarly in terms of detail retrieval and imaging coherence (which I thought was the weak point). Overall I really like them and am glad I have bought them. I'm looking forward to countless hours at my computer with these on listening to internet radio broadcasts and doing sound editing whilst being all but unaware of the noise coming from the computer itself.
