I use my AKG Q701's.

Sennheiser HD 579s and now a Focal Elegia that is new to me.

EPOS / Sennheiser GSP 600 (LAN set) or 
EPOS H6PRO
 
Both sound fantastic with the Burson V5i Op-Amps, although the originals were no slouch either.

EVGATech_LeeM

Poisonerka
Sennheiser HD 579s and now a Focal Elegia that is new to me.

Those Focals should be special.  I'm actually a bit jealous.

They're indeed incredibly awesome.  I was lucky enough to snag a pair that was in immaculate condition on eBay.  The best way to describe the experience is that its similar from playing a game at 720p on a toaster and then getting to experience at on a high end rig at 1440p 144hz. 

V-MODA Crossfade M-100

dialthegate
I fixed up my K7XX. Both it and my Sen HD6XX sound fantastic. 
Just ordered HiFiman Sundaras to give planar magnetic headphones a try. 
 
I had a little dot mk II tube amp hooked up to the EVGA nu audio's rca outs and there was so much interference and a noisy floor. That problem is not present when I use my JBL monitors nor a headphone splitter....so I will attribute to the little dot. I tried tube rolling as well and messing with the gain settings but couldn't NOT hear the interference. 
 
Ended up returning the little dot amp, I don't think tubes are for me.  

Hmm, I would guess there was either an issue with the little dot or the tubes themselves.  I've used the NU Audio Pro with both a Dark Voice and something quite a bit more expensive, and it's quite silent.  The exception is when one of the tubes went bad in my higher end amp, and this created all sorts of interference and noise until I either swapped the tubes and ultimately had it replaced. 
 
I've not personally tried the Sundaras, but I've used the Arias (V1) and they sound great through the card.  Admittedly, you'll probably need a dedicated amp to get the most out of those (you'll get sufficient volume, but there is only so much power an audio card can put out for planars), but it's still a great way to get to know how those headphones sound.

05/2021-"For Speakers I am using the Logitech z623 2.1 Speakers. Headphones I am using  DT 990 Pro's Black Ninja Edition's for my gaming and Music except for every high bass music, Audio-technica M50X For Bass heavy music and bought a pair of 1MORE Triple-Driver Over-Ear Headphones from Drop .com a month ago but their is a delay on shipping so I'm still waiting for those. I am swapped the headphone op-amp to LT1469 same as the pro. ordered two Burson v6 Classic's for both op-amps but there is delay on those also so still waiting. Damn you Corona!!" *Update 07/2022* It's been a year since last post and here is a update since then. Headphone still the same, I got 3 pairs. 1st pair is "Beyerdynamic
DT 990 Pro's Black Ninja Edition", 2nd pair is "Audio-Technica M50X" and last is my personal favorite. It has a very plain basic name and because of this these are very unknown and unheard of so it gets overlooked easily. They are called "1MORE Triple-Driver Over-Ear Headphones" These have Ceramic tweeters along with a nice midrange with driver that moves a separate woofer driver for deep clean base that feels like the same depth a that a nice 12" car subwoofer makes along with the tone.. 
Speakers are Edifer S350DB 2.1 PC speakers. If you do not know much about spreakers or audio cards you will need to spend a decent amount of money on higher end speakers and headphones/monitors. if you have a cheap gaming headset or headphones along with speakers you will not notice any difference in audio quality