I have the Phil's crossed over low at the moment, as low as the Marantz allows. However, they deliver in the bass department, as far as music goes. The Source Tech Trilines bring a bit more thump, but the Phils are more refined. Crossed over for subs and with material that doesn't have that natural ambiance, like movies, I think I actually prefer the Trilines just because I can blast them and never have to worry about about any issues.
Kef's are around $2000-2400 I believe for the R500.
That's crappy. IDK how large your enclosure is, or if it's sealed or ported, but the 10" CSS SDX 10" might be a good drop in replacement to reuse the enclosure. Plus it's a beast of a sub.