Bel Canto Mono Options for Center Channel

Since upgrading my main speakers to Verity Audio's I feel my center (Kef 204c) has fallen behind a bit. A new center is not in the cards (the Verity is $18,000, and I like my Kef), so I upgraded cabling (went to Transparent Ultra and ae24e).

I am also considering upgradin amplification. I am currently using a Bel Canto M300, and could consider going to the M500 or the M1000 (not the MKII), if a single unit shows up used. Would this worthwhile or am I wasting my time here? I don't need the extra power, but in particular the M500 is supposed to be better sounding? Should I look for the M500 or the M1000?