dynaudio confidence 5 versus contour S5.4

There is no way you will be satisfied with those amps driving the C5's - they will take all a stout 400wpc amp will deliver and more.

I've owned many pairs of Dyns, but never either of the pairs you're thinking of, so my input is at best an educated guess. I think you'd find the 5.4 a much more flexible speaker, and probably a more "fun" speaker. It has the later driver set, and is much easier to drive. The C5 is, IMO, a classic design, and probably has the potential to be the more accurate speaker.

If you've never heard the C3's, you might look for a pair of those too - I have owned those (a couple of times) and I really love them at their used price. They wouldn't be as demanding in what it takes to get them "right" as the C5's, but would share many of the same virtues.

I had looked at the confidence 5's for awhile too and my understanding from Mike at Dynaudio US is that because of there woofer alignment and physical placement on the speaker, they tend to have a lighter bass presentation then most like. Seemingly lighter then the 3’s, especially if you listen to stuff like massive attack you will miss the bottom end. kthomas also makes a very good point in that they need a lot of juice as you do really with any dynaudio speaker. With the ones that I have had, 175w DNA1 was ok but the 300w DNA2 was much much better! You will probably be much happier with the ported design of the 5.4.

IMO C5 is much better speaker than S5.4.Not even close.
To my ears C5 is even better than new C2 as I had a chance to compare them side by side.Agree that you need at least 250W
to drive them properly.
Hope this helps.