UPDATED (April 22, 2015):  See post #24 - http://forums.evga.com/FindPost/2325420
 
Having asked for and received the TB DPX21 for Christmas, I thought I'd give a few of my first impressions.  After much search over reviews between the top headsets I found the DPX21 to be a true winner.  This is my first Turtle Beach product and I'd certainly recommend it.
 
Let me start by saying the flexibility for customizations are vast.  The EarForce DSS combined with the PX21 are a brilliant combination.
 
The DPX21 supports the Xbox (all versions), PS3 and PC/Mac with and without SPDIF I/O.  It's a USB-powered headset (amplified).
 
First, I had it set up but figured out until recently it was using stereo until I switched the output to my sound card rather than the headset as before none of the controls worked on the DSS/PX21 as intended.  It made sense though, I wanted to output from my sound card using the SPDIF Out to achieve the 7.1 and use of the two systems properly.  After setting it up properly, I am wowed considerably.
 
In the DPX21 online manual, it says to turn down the Bass Boost on the DSS and turn up the Bass on the PX21 to prevent too much bass and ear damage.  Having the Bass option on the PX21 turned up and the DSS Bass Boost turned down is more than sufficient.
 
Quality of the headset is high - construction and sound performance.  It uses a fabric material and over long gaming periods of time, your ears will not hurt and not sweat as they tend to breathe well.  The weight of the headset feels light which is also a plus when gaming or listening to music for long periods of time as you don't feel like there's a brick on your head, a problem I read about with the Tritton AX Pro's.  Sound performance is amazing and as a first time Turtle Beach customer, I am blown away.  SPDIF I/O (digital) is the way to go in combination with the Dolby Digital encoder.  It brings everything to life as analog felt so bland.  You don't know what you're missing.  The highs, lows, mids including bass are extraordinary.
 
On the PX21, there's a slider to tweak the volume for Chat and Game.  Game volume will set the overall game/music/etc. volume (there's also another main volume on the DSS - setting half way is sufficient).  Chat volume will set how you hear others, some talk louder than others so it's good to turn it down sometimes.  There's also a Mic on and off switch.  And, there's an Expander on and off switch which when the Dolby Digital (DD) is enabled on the DSS, conflicts so it's good to turn the Expander off when DD is initialized on the DSS.
 
On the DSS, as previously stated, there's a main control knob.  There's also a Dolby Bypass button which gives you to bypass the Dolby Digital signal and use stereo.  When the DD isn't plugged in it uses the Dolby Pro Logic® IIx which reproduces full-range special effects in surround channels.  The DSS has the USB power input, SPDIF and headset inputs and outputs.
 
Cost wise, it's MSRP $149 + tax which might seem steep for some but totally worth it.
 

Tweaked

Thanks for the review.  How is the accuracy of the surround sound?  I didn't see this in your write up.  Does the headset use digital manipulation of sound fields to create the surround effects, or does it have multiple speakers?  Can you hear someone approaching from behind in a FPS?

Judging by this review:http://www.hitechreview.com/audio/headphones/turtle-beach-outs-ear-force-dpx21-universal-gaming-headset/28355/ it only has single speakers in each earpiece and uses digital manipulation to emulate surround sound.  That alone IMO,  would not justify a $150 price tag.

IMO, virtual sourround with 2 good speakers is better than trying to cram multiple speakers into one headphone.  
 
You only have 2 ears, positional sound doesn't work by adding more speakers like that for headphones.  It works in a room because there is room to physically place the speakers behind you but in headphones you only have the ability to place speakers right on top of your ears.
 
Your brain decides where the sound is coming from anyways, not your ears.  With the proper audio cues embedded into the sound wave, you get can get better position from 2 speakers in headphones.
 
Like this:
http://dc195.4shared.com/...0-591401a0/preview.mp3

I'd like to update this thread with another recommendation.
 
When using the headset with the PC/Mac, as this headset is USB-powered, I'd recommend using AC to USB power adapter instead of connecting into the PC or Mac itself.  This is because of interference.  When connecting it to the computer directly for power, I found when using a USB mouse, it produces audible static when the mouse is moved.  Having tried my brother's AC to USB power adapter in my UPS, it displays no such static. 
 
 
Edit: Fixed a grammar mistake.

Previously, I used the Creative Fatal1ty headset.  At the time, I thought that was pretty good until I went to something like this.
 
Using the Digital Out on the sound card, exhibits crisp highs, rich deep lows and great mids.

it would be great if u could come on team viewer and sort it for me :)
 

yes man my sound card is creative xfi professional , i have hooked all the wire up right as well man but only get 2.1
 

lol, I just sent you a PM to use TeamViewer too.

Good review, congrats on the BR :D

Hey just to let u know im back from spain hehe, i will wait for u to get intouch with me, you have been fantastic man i did not have time to say thxs as i had to catch my plane to spain look forward from hearing from u man see if u can solve this u r the best

sorry man been away from the keyboard watch the golf