[Eric_C]

Perhaps you could sell them cheap, since you got a good deal on them? Think of it as a way to pay the benefit forward.
 
Looking over your list again, I would also suggest you get rid of:
DT990 -- because you find other mid-low end pairs to be equal or better
Logitech H800, UE6000, and the Turtle Beach -- get a single, wireless, gaming headset that could replace all of these. I use the Skullcandy PLYR1 on my PC and Xbox and it's great. Jude (Head-Fi founder) loves it too.
All your in-ears -- except for 1 sport pair (for, well, sports!). Those IEMs you got all seem pretty average; I think you'd be much happier with 1 really good pair. Maybe the Westone UM3X, or Sennheiser IE80? 
 
Personally, I'd try to reduce everything down to 3 pairs: 
1 IEM for sports, 1 closed for travel, 1 non-portable for home use (doesn't matter if closed or open, as long as it sounds great)

 

[pataburd]

  Perhaps you could sell them cheap, since you got a good deal on them? Think of it as a way to pay the benefit forward.

Yes!  Sell them cheap to us Head-Fi vultures gathering overhead!  

 

[kraken2109]

I don't really see the need for more than 5, I'm sure you can narrow it down.
Some of them would benefit from an amp too if you don't have one (e.g. DT990, Q701)

 

[Cyberarhat]

Following Eric's advice, here comes the revised list of the sets I'm gonna keep for now:
 
Audiophile Headphones:
 
--Open back:
* AKG Q 701
* Beyerdynamic DT 990 Premium 32 ohm (burning-in, wanna give them a chance to prove themselves. Anyhow, they were                                                           recommended by the Wirecutter and come only second to the PSB M4U 1 for mid-                                                         priced sets)
* Sennheiser HD 598
 
--Closesd back:
* Denon AH-D600
* PSB M4U 1
 
Fashion Headphones:
 
* Beats Executive
 
Highly Portable Headphones:
 
* AKG Q 460
* Sennheiser Blue AMPERIOR
 
PC Headphones:
 
* Logitech H800 (wireless)
* Logitech UE 6000
 
Bluetooth Headphones:
 
* Jabra REVO Wireless Bluetooth Stereo
* Klipsch Image One Bluetooth On-Ear
 
In-ear Headphones:
 
* Beats urBeats
* Klipsch Image S4i Rugged
* Logitech Ultimate Ears 600vi
 
* Denon AH-W150BK Exercise Freak
* Klipsch Image A5i Sport
 
Notes: I have extremely tight ear canals, even for the smallest ear tips, thus I have a very difficult time finding a good fit from in-ears, inc. the pairs I already own. Guess I'll just have to stick to them. 
 
Gaming Headphones for Xbox One:
 
* Turtle Beach Ear Force XP510
 
The pairs removed from the list (V-Moda LP, Senn HD25SP, Monoprice Bluetooth, ATH-M50, etc.) are in a box now, waiting to be returned or sold.
 
Thanks, guys. You rock. I've learned from your replies more than I have in the past 2 months.
 
PS
 
Still, guys, from the list, which set do you think might provide best exp. with new age music? thank you in advance.
 
 

 

[Cyberarhat]

Thanks, Kragen. Already got Fiio E11 and E17. E7 works great, though for Denon D600, there's very minimal improvement in sound quality. Haven't even unpacked the E17 which seems to require a bit of learning involved. Been so busy with using http://www.tekfusiontechnologies.com/Burner/Burner.php to burn in the phones. 
 
Any thoughts on the upcoming AKG A 200 P? Here's the link: http://north-america.beyerdynamic.com/shop/hah/headphones-and-headsets/at-home/headphones-amps/a-200-p-us.html. It looks a decent product. After reading numerous Amazon reviews, it looks like Fioo has horrible, horrible customer service and warranty, don't want put too much trust in their products.
 
Consider my excessive number of pairs as learning tools for me to move towards being able to appreciate highest end gear, and I sure will settle with 3-5 sets. Extensive listening from various brands may be the thing I need for now.

 

[Cyberarhat]

Thanks, Kragen. Already got Fiio E11 and E17. E11 works great, though there's only minimal improvement in sound quality with Denon D600 amped up. E17 still in box. Been busy with burning in the phones with an online burn-in player.
 
Any thoughts on the upcoming beyerdynamic a 200 p? Looks like a decent product. I don't want to put much trust in Fiio, cuz from what I read from Amazon reviews, they have horrible, horrible customer service and warranty policy.
 
Consider the excessive number of pairs are learning tools for me to move towards being able to appreciate higher end gear and I sure hope I will then settle with 3 or so sets. For now, extensive listening on different brands may be the thing I need most.