Jet, if you don't have any significant budget restraints there's no problem with the separate amp proposal. Keep in mind though that the M80s are slightly above average in sensitivity and are by no means difficult to power. Especially with the EP500 taking most of the lowest bass load in a type of active biamping arrangement, either the 2600, 3805, or other similar receiver should drive the speakers with ease. In any case, the cost-effective route would be to try it first rather than assuming that more money needs to be spent.
