rel storm lll for my b&w 603 S2 speakers

The REL Storm III is a great sub. It will be better than your 603s in the bass department. That said, you could keep the REL forever when/if you ever upgrade your mains. There are folks using the Storm successfully even with the B&W Nautilus 804 and 805. If you do not think the Nautilus or something similar is in your future, the Stratus III is also fine for your 603s and you can save $500.

I am talking about music. If you want one for movies, then the REL Q series (Q100E, Q150E, etc) is even better for that, or the Velodyne.

You can't go wrong with the Storm. It's one of the most musical subs I've ever heard. If you use the high level connections the integration with the main speakers will be seamless.

Good luck!

I use a Rel Storm III with B&W Silver Signature 30s. I initially purchased the sub strictly as a home theater component and was going to switch it off for music. However, I must say that once I got it hooked up, positioned, and balanced in the system, it did a fantastic job... Needless to say, I don't turn it off for music. My dealer, whom I trust implicitly, steered me away from the other lines he carries for subs(B&W, Velodyne, Revel, etc...).