Dynaudio sub with C1's

That should work fine. Dynaudio make superb speakers. Their waterfalls are superbly clean and free of resonance - you will indeed need a good sub. The C1 midrange is not quite as perfect as the C4 but given you listen nearfield so I think the C1 will still sound much better. If you have a small room you will want the 300 otherwise get the 500 and your done....

What are you driving your C2s with? (I have them and unless you are looking for low 20s they have been nothing short of impressive on a Sim W8)

The Dyn subs are great; I have used a pair a sub 500s with the C1s and really enjoyed the sound.

Xtp16
If your Rel sub sounds slow its because of self induced stored energy. There are methods and devices that collect and disapate these resonaces. The stored mechanical energy will blend itself with any note to follow. These methods should be applied before you move away from the Rel to another sub. You may have never experienced the Rel in its full glory Any other sub or speaker would also benefit from the same applied method. Tom

Thanks for the response Shadone. My concern is that as great as the Rel is it doesn't seem to match up with the Dyn line. I was thinking if I change my intergrated with one that has a sub out would it be worth it to get the sub 500 to give me the kind of bass the C4's have. My room (living room dining room combo) is 27'X 16' and the setup is on the long wall about a 1/3 off center. I really don't have any other choice for set up (you would have to see my room to believe it - too hard to explain).

Yes I know it would work but I would just like to make sure the Dyn subs follow in the confidence line bass sound. It's several upgrades and a lot of $$$$'s.