Sennheiser 555s, with 600s on the way....what else can I get right now for under 300?

Got 555s and 600s now....

What other cans would be good to offer some contrast into this mix?

I am thinking about the AKG 701/702/ or AKG Q 701 Quincy Jones Signature Reference-Class....which one of these is the best one? theyre all the same price...

DENON AH-D2000 is this worth it considering my growing collection?

AT-AD700 or AT-AD900....which one or should I get either of them? I hear theyre the best for gaming performance using surround sound.

Beyer 990 pro, 600ohm or 250 ohm ?? do I need this?

Beyer 880\ pro, 600ohm or 250 ohm?? do i need this either?

I want to experience as much of the audiophile spectrum using 3 headsets maybe 4 or 5.

I ordered a Asus Xonar Essence STX w/ AMP built in, it supports up to 600 ohm. 

Do i need an additional external amp or is this enough?

my main focus is listening to Flac audio....and 7.1 virtualized gaming.

Nah dude...i guess you could say I just caught a lucky break on Amazon...

Already had the senheisser 555s from 2 years ago...

Got the S600 for a shocking 260 bucks off Amazon Lightning Deal. It was sold out almost instantly, then i was on waiting list for 40 minutes, then somehow my staring at the screen paid off...and it said add to cart now...you have 3 minutes to do this. 

Then, I went to newegg and got myself a Asus Xonar Essence STX, so that I wouldn't have to buy an Amp or DAC. This sound card has onboard that can power 600 ohm.

S600 $260 (free shipping)

http://www.amazon.com/dp/B00009QH7M (sold out now)

Asus STX $195 (173.99 + Newegg In-state Tax 12 dollars + 8 dollars shipping guaranteed 3 day ups (estimated 1 day))

Then....

I was trying really hard to decide between 3 headphones...

AKG Acoustics Q701GRN Quincy Jones Edition

vs

Beyer 880 PRO 600ohm

vs

Beyer 990 PRO 600ohm

(from what I can tell....the only differences between PRO and Premium, are the cosmetics, and it has nothing to do with the headphone itself).

vs

Denon AH-D2000 

(this one is somehow sold out EVERYWHERE except for amazon, where it is selling for:

"Denon AHD2000 High Performance Over-Ear Headphones"
Electronics; $339.95 +11.95 shipping
In Stock
   Sold by: ALO audio

I ended up getting the Denon, because of how highly rated it is everywhere...and how it is exactly what I need,,,in terms of high bass response. Reviews said it actually had pretty much the BEST bass response and deepest extension out of ANY headphone out there...and all this for under 400 bucks...IM IN!!!

Now, as far as I know...there is only 1 denon AHD2000 left...and its on amazon sold by ALO audio. Price is LOCKED at 349.99 EVERYWHERE...and yet its out of stock, unavailable, etc.

I do agree, 350 for a headphone is a bit steep for me considering I went on a big shopping spree this thanksgiving weekend, but this way I figure I will have a nice spectrum for myself...

1) A 600 OHM sound card with HQ sound to power anything up to 600ohm

2) Senn555 for gaming or everyday knockarounds

3) S600 for Flat smooth listening

4) Denon AH-D2000 for extreme excitement of BASS and high trebles 5-45k frequency response

(the Denons are even sold out at Denon's own website! how weird is that?)

So...

Now that I have this setup what should I get next?

I was interested in the AT-AD700, because people were telling me that it is the perfect PC GAMING surround sound headset when you use vitalization in the sound card...but I don't think I even need it anymore. The 3 headsets I have are technically better in every single way possible...so the AT is out as far as I know. (IF NOT TELL ME OTHERWISE)

Now...the reason I got the Denon was because the 880 and 990 premium Beyers cost 300-320ish on amazon, and that was the cheapest around I could find. There were PRO versions available in the high 200s, but they did not have 5 star ratings from headroom.com nor did they have as many fanboy reviews as the Denon did. Likewise....the 880s and 990s could not match the Denon's performance and overall frequency range....so paying 40 bucks more for a product in the next tier was a no brainer....i got the Denon first.

Now....I want a AKG Q701 quincy edition, for 250ish bucks on amazon. Or do you think I should rather get a 880 600 ohm? I hear most people say that the 880 is the best in the line, and that the 990 is intolerable. 

FYI my main focus varies from time to time....switching between hardcore PC GAMING (I prefer headphone virtualized surround sound to my 5.1 speakers) and listening to EVERY SINGLE KIND OF MUSIC in FLAC format through WASAPI foobar2k. 

Considering my current (or soon to be) setup, what should I get next?