Looking for advice re: amps for Dynaudio Contour 20i

Dynaudio need a powerful amp and they sound their best at higher volumes. 
I owned the S5.4 and drove them with Pass Labs X250.5. I also tried Rogue ST100 but the bigger Pass amp was better at opening them up. 

I would put the Parasound halo Jc5 on my short list.

Dynaudio is the US importer of Octave, and for good reason.  The two brands show together and sound incredible together.  Dyns can be a bit harder to drive so you need a black box or super black box with them but the results are going to be very, very good.

Alternatively, Hegel is a good choice with Dyn.  Clean and clear with speakers that are clean and clear.  Good combination. 

My take: You have two challenges to meet to permit your DYNAUDIO’s to max out their potential. I would suggest that you do it in this order

(1) Amplifier power ratings

DYNAUDIO craves high-current amps…. WPC alone are meaningless.
Another word on power: if your speakers are demanding to drive you’ll need a suitably muscular amplifier to support them. Don’t look only at the headline power figure - see what happens when the impedance drops to four ohms. If the number nearly doubles, then your amplifier has good current delivery and will be capable of driving more demanding speakers.

I would stay away from tube amps and stick with refined and beefy solid state options,

(2) System synergy matches

Now, because you have a much shorter list of contenders as you carved out the pretenders, you can now start the auditions and scope out reviews for that ethereal system synergy option tailored with your speakers.

You will get a plethora of amp model suggestions herein as replies to your post. But they have a high element of personal bias pushing their fave. Hopefully this simple matrix assists in assessing their recommendations as a candidate for your ultimate choice.

Thanks everyone! I appreciate the advice. akg_ca, last night I was thinking along the lines that you laid out - sort of like high torque / low revs vs. low torque / high rev horsepower; e.g., a 6 cylinder and 8 cylinder with equal power will never feel the same. I just don't know how to read amplifier specs to identify whether an amp is high current. 

I spoke with a salesperson who advised me that if I was unhappy with the sound, it had to be my speakers rather than the Marantz gear. Needless to say, I found myself struggling to give any of his opinions any credibility.