BuddTX,
The Pioneer A/V receivers use a current-limiting impedance switch for 4-ohm loads, which means they will deliver only a fraction of their rated output, or they may overheat and shut down.
If you have a Pioneer and want to drive Axiom floorstanders and realize all the power potential of the Pioneer, look at the Axiom M60ti, which is an easy 8-ohm load and is tonally virtually identical to the M80ti. The M80ti has a bit deeper bass extension and output (for really big rooms with separate power amplifiers).
If you don't have a Pioneer, then consider Denon, H/K or NAD, all of which will drive the 4-ohm M80s with no problems in rooms of average to moderately large size.
Regards,
