This is just a guess, but it might be that the EP350 dates back to before everyone standardized on always measuring in RMS watts rather than the many alternatives -- in other words the EP350 might have been 350 watts at the time, just not 350 watts RMS. Again, just a guess.

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8