the turtle beach px21 is a stereo headset. i have the turtle beach hpa2 true surround headset, which is discontinued. the successor according to turtle beach website was the z6a, but i just checked and that headset has been discontinued as well after a very short time on the market. the reviews on it were really bad in terms of durability last time i checked on newegg.
I looked at headests for awhile before i decided to fix mine after it broke (required soldering of 10 hair-thickness wires, 2 for each speaker plus microphone http://i5.minus.com/iDCIzxEIUgqzp.jpg) and i dicovered a few sets from cooler master featuring true surround sound that seemed pretty decent
Cooler Master CM Storm Sirus S http://www.newegg.com/Product/Produc…N82E16826570018
Cooler Master CM Storm Sirus http://www.newegg.com/Product/Produc…N82E16826570013
from what i was able to understand, the difference between the two is that the original non-S headset is the same headset but it is a bit more expensive because it comes with a reportedly, really nice control knob. if my hpa2's ever break for good, my first choice would be the "S" version because it plugs directly into your computer's sound card using the 3.5mm jacks for front, center, and rear sound. In the regular non-S version, the 3.5mm plugs go into the control knob which connects to your computer using a usb cable, which i would think uses its own sound system and removes any benefit of having a sound card/audio drivers.
I haven't used the cm storm sirus s, but my guess would be that it's is the closest thing to the turtle beach hpa2, which i can vouch for.
if the cm storm sirus s doesn't interest you, my advice would be to get a headset that connects to your computer using 3.5mm audio jacks, as usb headsets use their own built-in software that bypasses whatever hardware/software you have installed