I have Steelseries Arctis 5 headphones and prefer headphones for gaming especially for fps multiplayer. I responded to OP because it sounds like he is not interested in surround sound anymore but a 2.1 setup.
I agree with B00nie here, IMO, my two bookshelf speakers sound better than the Z5500 setup.If you have 1000 bucks to use, you can get a decent 2.0 and a horrible 5.1.
If you want a decent 5.1 you have to spend 4-5k.
A good 2.0/2.1 system will dominate a all in one 5.1 system when it comes to soundstage. A quality driver delivering sounds you won't hear out of a $2 quality center channel is a drastic improvement. Satellites in all in one systems are pathetic. Just get headphones for the price and be a happier person if you want cheap surround sound.
My personal belief is that a 2.0/2.1 system of quality gear will be a vast improvement. I use Mackie powered monitors and the wonderful Polk 10" subwoofer. I say wonderful cause at $100 it can't be beat pricewise in small deployments. I bought my dad Presonus 4.5's and they are equally as good. That said, I would not recommend the current mackie monitors as their quality has collapsed after the EAW/transcom nonsense. Presonus or KRK are the others I have experience with and liked. Presonus probably over KRK. I have not used Yamaha, Edifer or other popular budget friendly models so I can't suggest those in faith.I was thinking of getting like a pair of audioengine a2plus or a5 or a presonus 3.5 . Then get a separate sub . would those sound better than what i have currently?