I am not much for surround sound, but find my set up ok. - I know it wouldn't suit a movie buff.-
You'll get better advice here if you give a little more info. What amp do you have? I see you have tannoy speakers. Would you need floorstanders, or do they need to be smaller bookshelf type.
A sub can probably be run from any amp but an amp witha dedicated sub out is probably prefereable. I recently bought a monitor audio a100, that has a sub out, though it is mainly a stereo amp, so an amp with a stereo amp with a sub out is possible.
Depending on your amp, a better set of speakers will likely go a long way to curing your problem
EDIT- Your speakers are active oops
Everything else I said holds through though. If you need an amp witha sub your choices are a stereo amp or a surround sound amp. I think it is generally considered that stereo amps are better for music unless you really spend a lot on a surround amp.
One thing though is if you buy any recommended amp, it will likely need digital inputs to feed your bluray/dvd/ sat box into. I'd look into something like the Yamaha AS701 and possibly q acoustics concept 20 with q acoustics subwoofer as a start