Tritton AX Pros are a horrible headphone. I borrowed a pair from a neighbor for an evening and took them back after about 15 minutes. The sound quality, going through their little sound processing box, was hideously deficient. The "surround" sound speakers are small and sound worse than apple earbuds.
There was also an audible hiss or buzz no matter HOW I hooked them up (S/PDIF, av out, MixAmp, etc. I tried about 6 different ways and ended up quitting because no matter what I did there was some type of feedback on top of the worst surround experience that could possibly be produced.
Get simulated surround headphones, they sound WAY better with larger drivers and a much better sound stage. 5.1 headphones don't work near as well as a decent set of 50mm drivers and Dolby Headphone.
And, BTW.... the sound card was not needed. The headphone processor handles sound. You don't need both. You have the sound card processing sound and then sending it to a REALLY crappy surround processor to be processed again in that goofy box/cable mess that is the Tritton twisty cable mess of crap. This is probably why you are getting the echo. The design/implementation of the AX Pro is terribly flawed and it is built with very substandard speakers, connections, components. And, the surround processor is not very good.
Honestly, get a good set of regular headphones and a good sound card. I use:
AKG Q701 w/ Astro Gaming MixAmp via motherboard optical for Dolby processing:
http://www.google.com/#q=akg+q701&hl=en&prmd=imvns&source=univ&tbm=shop&tbo=u&sa=X&ei=i2KcT53YNoXAgAfk8oWeDw&sqi=2&ved=0CGgQrQQ&bav=on.2,or.r_gc.r_pw.r_qf.,cf.osb&fp=74a09fdcf54f77ed&biw=1843&bih=962
and
http://www.google.com/products/catalog?hl=en&ds=pr&pq=akg+q701&cp=4&gs_id=1f&xhr=t&q=mixamp&bav=on.2,or.r_gc.r_pw.r_qf.,cf.osb&biw=823&bih=226&wrapid=tljp133564891046626&um=1&ie=UTF-8&tbm=shop&cid=7315912959758942594&sa=X&ei=rGKcT6rqJJSugQf66ID9Dg&sqi=2&ved=0CGYQ8wIwAA#
This setup probably costs about what you paid. Sounds MUCH better than any 5 speaker setup could, has WAY fewer cables to deal with and is more versatile. Note, 5.1 headphones DO NOT WORK. Positional audio queues simply don't hit your ears the way they try to do it. Dolby headphone processing out of two 50mm drivers would be MUCH more realistic (see links below).
It sounds like you want to smartly invest in a good audio experience. Go on Head-fi.org and dig around for their gaming setups. Or, you could go full on Astro gaming w/ their headphones and get a MUCH better experience, but not quite the realistic soundstage asn the K/Q701s.
Some view and info on the AX pros:
http://www.head-fi.org/t/525737/tritton-ax-pro-surround-sound-amplifier-compared-to-mixamp
Hissing/popping in AX Pros:
http://www.head-fi.org/t/592789/any-3rd-party-amps-available-for-tritton-ax-pros
Once you get a good sound setup (hint, you can't get it at Best Buy) your life will be SOOO much better. It is like sleeping with fat ugly chicks all your life and then bedding curvy hot midwest farmer's daughter that is into the freaky stuff. I mean, really..... how can you go back?