The RXV 1500, 750 and 650 are all in the same product line. The seperate product line referred to is the HTR series from Yamaha, normally carried at Best buy and other big box stores.

All three of these models have an assignable surround back channel to use as second zone amplifier; one or the other, not both. The big advantage of the RXV1500(over the 750) is it is THX certified and has more inputs(both 1500 and 750 have component video upconversion and auto setup), the 650 lacks the parenthetical features but can be used as the original post described his needs to be.