Most 5.1 PC Headset (the ones with 4-8 speakers) need 3-4 3.5mm connectors to give you the "full" 5.1. As the G74sx only hs a stereo headphone jack the only way you could run this is through a USB sound card.
have a look athttp://www.amazon.com/Tritton-PC510HDa-Powered-Surround-Headset/dp/B004W7PHVO/ref=sr_1_1?ie=UTF8&qid...
Some like the Cyber Snipa Sonar 5.1 Championship Headset and the Trust 17554 GXT 26 5.1 Surround USB Headset use USB so you don't need any extras. I have never used them so I don't know the quality.
As for 7.1. I maybe wrong but there isn't a true 7.1 headset especially for under $100 (they are all "virtual" 7.1).
I use the Logitech G930 (USB and software), they are OK. My experience goes like this...
*Had to replace the first pair as the volume wouldn't go up with the in built volume controls.
*They are a bit bulky for transport (don't really fold down much).
*Your ears can get warm sometimes.
*The 7.1 is fantastic ONLY when you use the in software demo. all other time its OK, but (in games) hard to notice (if at all).
*The can click and beep a bit if they are on but no sound is playing.
*Can't wear my 3d glasses and the headphones
*The sound quality is overall very good. The write ups are brilliant.
*They are wireless which is a bonus. with 20 hour battery life (best I see is 10 hours).
* They are comfortably, they use memory form, they are not that heavy and to be honest I forget I've got them on.
*They have 3 quick button on the left this can be changed to be used in individual games i.e to attack, pick up, bring up menu and you can customize them for the game or windows player... or whatever (I have never found a need for them as touching the keyboard is always going to be quicker than touching your head!).
*All the controls are on the left so you can keep you hand on the mouse.
*The in house software has lots of options.
*They look good
*You can use and charge.
*hard to hear anything over them.
*The Logitech G35 are wired, cheaper and have interchangeable padding (don't know if they are memory form)
I brought mine because I have a Jamo HTS which is awesome. Only problem was when my misses wants to watch Downtown bloody Abbey, sodding Twilight or 16 and up the duff. I can retreat into a MANLY MANS world of blowing up stuff and driving fast.
For that they are great, but I would never use them instead of my S606's.
Hope this help. I looked into A LOT of headphone and for the money these seemed the best buy.