Yeah, the AX720 isn't the BEST. I'd say it has 100% of the performance of the Mixamp, just with HISS. Still, it's a much easier setup in the home, you can buy it locally (and return it if you don't like it), AND you get a free headset. I don't think the headset is that bad. Certainly it phails when compared to any headphone known to be good for gaming, but as an all in one solution with people who don't have anything, the AX720 headset will do them much more justice to their gaming over no headphone/headset at all. It's MUCH better than using TV speakers or stereo speakers.
I have all 3 in the house (my roomie owns the AX720).
-Get the Wireless Mixamp 5.8 if you can afford it. 99% the same as the wired mixamp, maybe just a LITTLE brighter, but with a bass expander button which adds a very subtle amount of bass
with zero tradeoff. AT extremely loud levels, the 5.8 has some very slight hiss, though doesn't approach the hiss of the AX720.
-Get the wired Mixamp if you don't care about cable clutter, just pure SQ.
-Get the AX720 for the same price as the wired Mixamp. Can be bought locally. Just take note it has an audible hiss during quiet scenes in gaming. You get a 'decent' headset with it. I'd personally use the headset as a backup. I had no problems kicking tail in CoD with it. It does it's job.
I'll be honest, if I had known about the AX720 before I got my A40/Mixamp combo, I would have went for the AX720 instead. I prefer a cleaner setup than less hiss.
-Get the Turtle Beach Ear Force DSS. Can also be bought locally at Best Buy. It's the cheapest DH solution, BUT it doesn't allow for voice chat unless you own a Turtle Beach headset. If you want voice chat, you'll have to buy the Steelseries Spectrum Audio Mixer. Both together cost about as much as the AX720 or Mixamp, is a LOT more clutter, and inferior SQ (the Audio Mixer has pretty bad hiss). It's also an ugly solution.
Still, for those who aren't gonna use a mic...ever, the DSS is the most cost effective solution.
If I remember correctly the tritton amps need to plugged into the wall, which for most maybe isn't ideal. Much easier when things plug into USB, isn't that what they're there for. I'm sure it doesn't use that much power it needs to be plugged into wall.
Astro mixamp seems like the best choice for convenience if you buy an optical cable.
The Mixamp 5.8's TX unit also has top be plugged into the wall. The good thing about the Tx and AX720 is that they can stay hidden, whereas the wired Mixamp HAS to be near you. This means you'll need a pretty long optical cable (as well as USB cable if you're not using the battery pack) between you and the console. I for one did not like having both an optical cable AND usb cable ran across the ground to where I'm sitting.
With the AX720, all you need near you is the cable that has the AX720's small puck that has everything you need. Just ONE cable with volume control, voice/chat leveling, everything. Think of it as an inline Mixamp. I just wish it didn't have the hiss.