I disagree with those who suggest a sub is just for explosions and crashes. REL has a great reputation, it should be a good addition for your Dynaudios. The mistake many make is in the set-up. I find that setting the crossover too high at first makes it easier to find the right phase adjustment. Then set the crossover and output levels too low and inch your way up. When properly tuned in, you should be almost unaware of your sub- until you turn it off. Although there can be benefits using the crossover to cut the lows from your main speakers, I usually like running the speakers with fullrange signal, you may experiment with plugging the ports.
If you get a good price, I definitely say go for it. You may love it, the set-up can keep you busy in a fun way, and if it doesn't work out? It's a REL, and should be easy to unload.
If you get a good price, I definitely say go for it. You may love it, the set-up can keep you busy in a fun way, and if it doesn't work out? It's a REL, and should be easy to unload.