If you were thinking of buying any other subwoofer besides a REL the results would be questionable, but REL subwoofers don't sound like subwoofers. A REL will produce clean musical bass that will complete your system. You won't believe what you've been missing. Granted, your Dynaudios may be rated to 40Hz, but those little mid/woofers just don't move much air.
You've got nothing to lose. If you don't like it REL's are easy to sell. I say go for it.
You've got nothing to lose. If you don't like it REL's are easy to sell. I say go for it.