Use the Yamaha for now, and get a Peachtree nova 150 or 300 (depending on how loud you listen and how much bass content your average choice of music has) to run the front two in Home Theater Bypass mode. That way you have a simple two channel dedicated rig (that sounds amazing and has more than enough grunt to power them), as well as an external amp for home theater that will relieve a lot of stress off the Yamaha during movie watching.
If you have a sub or subs, the external amp will likely have no effect during movie watching as long as you have all speakers crossed over to the sub as you should. Unless you are in a large room and listen painfully loud.
If you have a sub or subs, the external amp will likely have no effect during movie watching as long as you have all speakers crossed over to the sub as you should. Unless you are in a large room and listen painfully loud.

