There was this review in case you missed it :
BK XLS 200 Subwoofer Review (Long Post)
I have used mine a lot since getting it on the 23rd Dec 2003.
Have it hooked up via low phono.
For films I couldn't be happier, can easily cope with short sharp explosions to prolonged rumbles and the like. Only used it with gain around 50% and it provides plenty of kick in room 24x18 with 13ft ceilings.
Music - I find it compliments my speakers perfectly now I have fiddled about with settings and am accustomed to it. IT has filled out the sound perfectly and cds i used to think were a bit trebly are now far more enjoyable to listen to.
With music it definitely adds more power and depth if you get me and sounds as good with heavy rock or quiet acoustic tracks.
I would say it is probably at its best for Cinema as it integrates so well (with my setup at least)
When you have it setup correctly you wont notice it being there - mine doesn;t boom at all even at around 60% gain - as I said, It genuinely has filled out the whole sound without being the slightest bit obtrusive.
I think if you are in doubt whether to get one or not then look at what else you would get for the price up to £500 and I think you'll find it hard to find anything better.