If you're in a position that allows you to spend a few hundred dollars on an audio system, you really ought to do it. I think it is the most often overlooked, critically important part of a gaming setup. A lot of resources are spent on making modern games sound great. You need to spend some resources on your end to get the payoff.
The biggest jump comes when you go from TV speakers to just about any kind of discreet audio system. It's night and day difference. You can of course keep getting better and better from there. But, that initial improvement in audio performance that you get when you get rid of the TV speakers is huge.