Thank you for this Mad Lust. This is a minefield for relative newbies such as myself. I nearly just gave up and settled for some A50's because it was easy but glad I didn't. I definitely want Dolby Headphones so will be getting a Mixamp, it's a toss up between DT990 (250 ohm) and Fidelio X1. My current reservations are, DT990: reports of harsh treble and listening fatigue, wouldn't get the best out of them with the mixamp and I do not know if it's possible to have Dolby through the mixamp which is somehow connected to a DAC/AMP like the Mav Audio Tubemagic which I would import. the plus side is the phones are about £118 comapred to £180 for the Fidelio BUT would require the extra AMP/DAC purchase thus negating this bonus.
The Fidelio seem to be held in high regard, I belive would be fine through the Mixamp as they are 50 ohm (may be wrong here) and thus would't really require the extra DAC/AMP purchase, Despite costing £60 more this would actually work out cheaper as no extra equipment needed.
I rarely listen to music through headphones and this will be purely for my PS4 gaming, not movies.