Ben.
You don't want big speakers if you want 'rumble' you need a dedicated sub. I have a tannoy 5.1 speaker set in the living room
http://www.superfi.co.uk/index.cfm/p...roduct_ID/6211
It's crazy, more suited to films than music, but is still decent with 2 channel cd music. If you crank up the sub, it will literally shake the floor, scares the pants off you in some films
As said, get yourself to richer sounds. A 5.1 system for movies and games is very different to a system just for music. I've never bought floorstanding speakers, I've had lots of quality 2 channel stand mounted speakers in my hi-fi systems, and never felt the need for anything bigger. You'd be amazed at how a £200 pair of stand mounted speakers sound with a good amp and source.