Just to understand better are you using the 665 to drive your theater and using the zone 2 to drive these other speakers?
You could use any 2 channel amp rated for 4 ohm loads. I use an Onkyo M-282 but you could use a Behringer, emotiva, rotel, etc. I would look for a good used amp that you may find here or craig's list, ebay or audiogon.