Dynaudio Contour S5.4 or Confidence C2

I have my C4's in a well treated 15' x 21' room. I don't think a 13' x 15' room is large enough to let the C4's breath, as they really need to be pulled away from surrounding walls to sound their best. If you want to stay with Dynaudio I'd look at C2's or C1's with a nice subwoofer. Both of your amps would work fine either way.

Pdreher is right regarding the C4's. You will never really hear the full potential of the C4's with your room. Have you demoed the C1's with a sub? You may be surprised.

I agree with the room being to small for those C-4's. I never owned them, but after interacting with other C4 users, they can be difficult to place for bass and the more breathing room, the better. They are stellar Dynaudio speakers. If you like the Confidence line, I'd suggest as others have the C1's or C'2s. You may even want to explore the Sapphires, but they are more costly. The Sapphires do work well in a smaller room. Your amps are quite fine.

13' x 15' room?

Honestly, I am really surprised that you are getting good results with the 3.3. Do you not have major bass problems in your room?

I had S1.4s in a 14 x 16 foot room, and they were great, but completely overpowered the room in the bass.

with 13' x 15', the C1 is your ideal speaker. it has bass down in the low 30s for you. try them out, several pairs on a'gon. if not enough, go further up the pipeline.

but C4s are definitely out of the question for you---refer to stereophile review for more information.