First, hello and welcome!

I'm not intimately familiar with the entire line, nor your budget, but for those speakers, I would recommend something from the REL line.

I have heard much of the line and like them, and I have never met an audiophile who wasn't happy with them when purchased.

Examples of their more affordable line.

I think the REL's are good at "fast" which would mate well with your current speakers.

I'm sure others will have good ideas, as well.

I've heard very good things about the Epos subs, which they themselves state that the "music" is the goal and not the special effects.

I have a Cambridge Sound Works sub for my 6.1 system that is quite musical as well. Overall I'd say go with smaller subs as they will be faster and produce tighter bass for you.

I'd too highly recommend looking at a REL subwoofers. Their ability to expand the soundstage is remarkable. They integrate more seamlessly than any other sub I've heard. When properly set up the sub is not a source of audible sound, it just sounds like the left/right speakers have had a major increase in bass extension. Of course that sounds like a description of what ALL subs do, unfortunately they don't. RELs are the perfect sub for those who want musical bass, that perfectly matches what a great speaker can produce.

Congratulations! You've purchased a nice product from a great company. Let us know how it goes.