afaik the behringer 50watt amp can power (2) 4 speaker cabs (left and right) without any trouble and will sound very loud, also as a comparison the beatles (and alot of other people) used/use vox ac30's which are 34 watt amps, and they are deafening past 5 on the volume.
on another note isnt the 50watts mentioned (speakers) their max output ? going over 50 or even getting near it will damage the speakers and cause them to blow (especially if they are old), the speakers in my amp(2 of) are rated to 110watts yet the amp is only 60watts to both channels (left/right).
correct me if im wrong here. :D