Medusa 5.1 surround sound headphones all the way. There's both USB and soundcard versions. Each has a sound cancelling mic too.
Not cheap at around $120, but the situational awareness you get with true sound sound is amazing, even in AH. When I can hear someone attempting to climb up on my blind spot on my six, and I can even hear bullets whizzing by on the right or left, I sometimes start thinking it is an unfair advantage.
Only sometimes, though. ;-)
-Llama