I can't imagine needing an amp. The 2400 puts out 120 watts/channel. Of course it's debatable how much it can continuously put out on all channels simultaneously.
However Axiom speakers are quite efficient. The M80s are 91db (anechoic) and 95db (in room). As others said, anybody who has used a receiver/amp with power meters on fairly efficient speakers can testify the needles hardly budge off the pegs, except under extreme conditions.
Years ago I had an old Sansui 8080 receiver with front panel power meters. It drove efficient Pioneer HPM-100 speakers (bass reflex design). 0.05 watts was listenable, 0.1 watts was loud, 1 watt was extremely loud. Over 5 watts was punishing -- entire room would shake, and you could hear it outside two houses away.
If you want to make a real difference you'll hear, put your money into a nice SACD/DVD-A player and invest in high quality multichannel material. E.g. whether anybody can hear amp differences in a controlled double-blind test is often debated. But anybody can hear the difference between a stereo CD of Pink Floyd Dark Side of the Moon, and the 5.1 SACD version played on your system. The difference is simply vast, and likely not simply because of the high resolution sample rate. Rather doing a quality re-mix, quality transfer and going from 2 channels to surround makes the difference, at least when properly done on fitting material. You've described a nice system; I'd suggest getting material that fully utilizes it.
Likewise room acoustics can make a big difference. For the money you'd spend on amps you could do some acoustic treatment. Depending on your room, this could make a profound difference.
If you already have good room acoustics and lots of quality multichannel material, I guess you could get the amps if you like them.
