[Zippy0]

I am primarily using a Hifiman HE4XX and Phillips Fidelio X2 with an Aune X1 MK2 Mini Dac. I also got a Rega Ear R for really power-hungry cans.

I am simply looking for a full-sized closed-back headphone that should be comfortable, not have fatiguingly dominant highs and the cable has to be changeable.
I was looking at the Fostex T40RP MK3 plus some different pads for it for example.

What are some good options in that price-range?

 

[serman005]

Maybe read about a Meze 99 Classics and see what you think. It is possible it could work for you.

 

[surfgeorge]

The Meze 99 Classic are a "classic" pick in that price range, but I ended up with the Audioquest NightOwl, which has an MSRP of €699 but can currently be found for little above 300 on Ebay, since AudioQuest has given up it's headphone product range. Contact me if you need more info about the seller.
Soundwise the NightOwls create a deep soundstage, are very smooth (very low distortion) but punchy, have clear but also smooth treble and come with 2 pads which let you adjust the sound a bit. They are a bit dark, but after adjusting to their signature they create a very realistic experience, especially of settings like jazz bars or concert halls. Their imaging is also very good for a closed headphone. Pair beautifully with the Chord Mojo.

They need a lot of burn in though. If you are interested, search for betula's review of the NightHawk, NightOwl and the 3 different available pads.
Those headphones are also extremely comfortable.

 

[bixby]

The Fostex are not that good. Above your range, E-Mu teak, below Senn HD-569