There is a discussion about this in the current thread on the 20.7's. I think you will find that lots of people have opinions on this subject. I have no experience with biamp'ed 3.6's using an external active crossover, so I can't offer a comparison on that set up vs. a stock 3.7. Those who have that set up appear to be very satisfied, so if you already have the amps and the crossover, it might make sense to go that way.
A separate question is the comparison of stock bi-wired 3.6's vs stock 3.7's. It seems that some have a very strong preference for the 3.7's, while others are less enthusiastic about the magnitude of the improvement over stock 3.6's. I have gone the monoblock route. I find my 3.7 single wired to my Cary 500 MB's to be wonderful. If your stereo amps are matched and can be bridged, that would be a way to fully utilize your existing equipment with the 3.7's.
A separate question is the comparison of stock bi-wired 3.6's vs stock 3.7's. It seems that some have a very strong preference for the 3.7's, while others are less enthusiastic about the magnitude of the improvement over stock 3.6's. I have gone the monoblock route. I find my 3.7 single wired to my Cary 500 MB's to be wonderful. If your stereo amps are matched and can be bridged, that would be a way to fully utilize your existing equipment with the 3.7's.