Interesting question. A couple of years ago I was considering the Avantgarde Duo and lugged my Cary 805AE's into a dealer for a listen. There were more than a few issues with the way the dealer set up the speaker - room too small, did not get a good match between the subwoofer and the horns, etc. But I discovered that the amp was a very good match for the speaker.
I got to listen to another Avantgarde with a variety of different amps, and was surprised by how sensitive these speakers are for quality amplification. An Audio Note Oto SE simply sounded dull and lifeless. A Graaf 20W OTL sounded much better - more detail and better dynamics, but was a bit too forward.
The Cary 805AE was in a different room, so not strictly comparable. But the dynamics were something else - VERY impressive. The tone was typical Cary 805 - a touch on the bright side, magical top end, and very sweet.
I am not sure how the 805C compares to the 805AE, but I think it would be a good match.