Well it depends, are you just going to do mame and other emulated arcade games, or pc racers as well? While there are some arcade games that had surround sound, I don't think any of the emulators implement it properly. Normally for arcade games I don't like a subwoofer, but racing games are different. If you stick one under the seat it feels like engine vibration and a lot of real cabinets actually did something similar.
Hope that helps.