"I recently purchased a pair of B&W CDM1 SE for a steal on Craigslist, and while the treble is more detailed, they don't sound as good overall as the 602's. I have also tried a new pair of the B&W CM series and there was a very marginal improvement in clarity and image, but not enough to justify the cost difference, so they went back."
If you're doing a horizontal biamp, try it vertical. I will probably sound a lot better. If you still feel the need to get new speakers, DeVore makes a really good pair bookshelves. Sterling is another good one.