The 600 S2 Series is a a step up from the S1. The tweeter is smoother and a bit more extended. In fact, the 685 S2's can hold their own very well inmho. Moreover, the 600 S2 Series uses the same exact drivers as the CM S2 Series. Of course, the CM S2 Series have better cabinets/finishes and better quality X-over components. However, the newer 700 Series is a significant jump from the CM S2 Series altogether. But as has already been mentioned, the pricing is ridiculous.
In short, the BMR's own the under $2K market and still punches well above that range. In other words, you would have to spend some serious money to best the BMR's which would be no easy feat. Dennis has mentioned many times that he makes like $6 an hour doing this. We are very lucky to have him here. Just saying.............
Cheers,
Phil