[PurpleAngel]

  OK, after reading some more and narrowing my budget, here's the final showdown (all prices listed are the lowest I found to get them ordered here to Croatia, EU):
AKG K702 - I can get them for a total of £151.72 via Amazon.co.uk
Sennheiser HD 598 - I can get them for a total of 181.41 EUR via Amazon.de
Beyerdynamic DT 990 Pro 250 Ohm - I can get them for a total of ~ 152 EUR / £120 locally here from a shop in Croatia.
(only concern for these is can my amp , the Pioneer VSX-D814 drive them properly)
So, taking into account that
- these will be used with the equipment mentioned in the OP;
- purely for gaming use;
- where other than the actual sound quality, COMFORT is the main parameter (long gaming sessions ,etc.)
... which ones should I buy and why? 

 
Your Pioneer receiver uses the same amplifier(s) to drive the speakers and the headphones.
So if it can drive the big diaphragms in a speaker, should have no problem driving the little diaphragms in headphones.

 

[capac]

250 ohm beyers won't be a lot easier to drive than k701/2. Any decent amp should do the job just fine with AKGs. And who cares where AKGs are made, they are still well built.

 

[Iv4nI]

Hey everyone! In the end I went with DT 990.
Great price + managed to try them in store before buying and they're super comfy and sound great. 
Decided against the K702 because I couldn't try them in store anywhere and was worried that my current setup wouldn't be good enough for them. 
 
Anyway, thanks for putting up with me. Now I'm set.

 

[cel4145]

Congrats. You got some great headphones