Welcome to the forum. Very comprehensive request! Can I ask do you have an external DAC/headphone amplifier already please?
This can make a real difference to a. sound and b. choice of headphone. At first pass, however, I think you should try the AKG 52.
Do let us know what you eventually get...
A quick search around the site and people are recommending a Synology NAS (EDS14 is around £200), easy to set up and supporting apps via iOS.
Hope this helps and do report in.
I've never heard of them, but, remember the weak pound and the potential for customs to both slow things up and take another chunk. They look nice so I've found a distributor here for you, worth checking out UK prices first?
http://www.nunudistribution.co.uk/products.php
...why does everyone talk, and now write with sentences starting with 'so'. That's, like, kinda American. Totally.
B&W P5 hands down for the money and the recent price drop.
....not for bassheads. However, I don't consider myself a basshead but just don't like the *to my ears - lean-sounding AKG 'house sound'. Some would call that neutral. I prefer my Beyer DT990 250 Ohms instead.
http://goodmath.scientopia.org/2011/12/30/audiophiles-and-the-need-to-be-special/
Why not buy some cables like these too?
http://www.audioemotion.co.uk/vertex-hires-speaker-cable-8405-p.asp
They really will bring out the detail, soundstage and your golden ears will love it!