I have both of those items, so I could give it a test drive for you this weekend, if nobody else has tried it.
Yeah, that would be really appreciated!
Also, how do you think the NAD Viso HP50 compares to the Philips X1?
Personally, I like the X1 much more. I find them both to be fairly "thick" sounding headphones... the HP50 even moreso than the X1. X1 has more impact, which makes it more fun to listen to. The HP50 has better bass extension, but I wouldn't call it a basshead headphone. It's quite full sounding and fairly neutral, but again, a bit thick in the midbass and lower mids.
The HP50 can be a touch shouty toward the center of the midrange, a trait it shares with the HD650 and the stock HE500. I find that I am generally more sensitive to this than others, so it may not be a concern for you. The upper mids are well balanced, bordering on relaxed. I find the X1 to be a touch more elevated and pleasant in this region. The highs are bit relaxed on both, and sibilance is very rare. Overall, I'd say the HP50 sounds a bit dulled out on the top end (but not veiled), whereas the X1 is a little more crisp and lively.
Soundstage and imaging are very good on both. You get a couple of 'outside the headphone moments' with the HP50, which are quite impressive for a closed back. It really seems to defy the closed back design sometimes, especially with movie scores. There is a nicely defined bubble for the sound image. I feel like the X1 is more organic in its soundstage presentation overall, being an open back, but the gap with the HP50 isn't as big as it is with some other closed backs.
The X1 is better in terms of comfort. The HP50 is hit or miss. Sometimes it's very comfortable, sometimes it's not. I think it really depends on how you situate the pads on your ears. The X1 is certainly the prettier of the two. The HP50 has this weird square Frankenstein head top, which I find a little odd. I recommend a cable replacement for both... the HP50 cable is too short to be practical for anything other than mobile use.
Overall, I find the HP50's sound to be very even and well rounded, but a bit boring. It does a lot of things right, but it doesn't do any one thing so well that it inspires any passion about the headphone (for me). The X1 wows you with its combination of punch, impact and soundstage, and then seals the deal with its ability to be both smooth and detailed on the top end. The HP50 doesn't really wow me in any one area, it just does everything well.
TLDR version: If you are looking for a warm, balanced headphone with solid delivery on all the fundamentals, the HP50 fills the bill. If you want a headphone that will excite you and or add some sort of definitive aspect to your listening experience, you'll probably be disappointed. As always, YMMV.