Subwoofer recommendation needed

[Randomshat]

I have B&W DM604S3 front speakers, DM603S3 rears, and a LCR600 centre.

I want to add a sub, does anyone have any recommendations for a good match? I would rather add a sub than replace the speakers, as despite their age they sound great

 

[bigboss]

What's the room size? What's your budget? Is this for movies mainly, or music as well? Sealed or ported?