On page 9 of the user manual:
http://www.adcom-usa.com/gfa-565se/ask-3
All loudspeaker systems having a nominal impedance down to 2 ohms can be connected to, and driven by, the GFA-565SE. The GFA-565SE can drive these low impedances at more than adequate power levels with no difficulty. lt should be noted here that many loudspeaker systems which are rated, nominally, at 4 ohms drop in impedance, in some parts of their frequency range, to as low as 2 ohms (and some others to even less than 2 ohms). You will not experience difficulties even with these very-low-impedance loads.My guess is 8-10 watt in class A, you can ask Adcom:
http://www.adcom-usa.com/gfa-565se/ask-3