With the M60 the external isn't really necessary since it is relatively high 6 Ohms. You'd save a fair bit going higher power receiver with better processing. just keep an eye on your AVRs heat level.
When I switched from bookshelves to M80s my AVR{Teac Pro} was getting really warm from there I scored a used pro amp 450wpc. that I enjoyed very much since have added a 3 channel ADA1250, I wanted to keep the same power level 450wpc.
Although you'll probably find the E.P.350 to be limiting factor as the towers put out wonderful L.F.E. levels.
On a plus note young kids shows are very musical they will notice their shows sound wonderful and we can sing them the originals along with the songs. {Backyardigans does a lot of old remakes} My kids are 7 and 9 when their friends come for a movie they have never wanted to leave. "It's like our own theater" I've heard many times.
Cheers
