Dynaudio Contour S5.4 or Confidence C2

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.

I had the C2s for over 4 years and loved them, but they too need room to breath, and show off their great soundstage.

I heard the C1's this past weekend at the AKFest show and thought they, with the rest of the system, was excellent; one of my two favorite rooms. Clearly a great match for the smaller room; I was told they tried a larger version, I didn't catch which model, and the C1 easily performed better as it was a better match for the room.