I've tried with surround, but I like headphones better.
To add to what dark said, I always look around a lot while on foot and listen.
The mantas are pretty quiet until they are REALLY close... and unless you are looking in that direction of have incredible reflexes... they will getcha.
When you dodge jump, double jump, etc.. you can turn in any direction while in midair and it will not affect the direction you are traveling, which is another advantage to dodge jumping around instead of just running.
There is also a way to disable your own footsteps in-game, works very well for DM/TAM. just google "disable footsteps ut2004" and there's a few guides on how to do it