You ain't getting a 5.1 for 80E, not even for double of that.
Microlab Solo 6C would be a good option for you.
Also, just set sound to 7.1 in games, leaving it as 2.0 in Windows. Providing your sound card is any decent (X-Fi HD / X-Fi Titanium HD / Essence ST / Essence STX / other things like that) it'll sound awesome.