Surround speakers typically don't need a ton of power, they are used for atmospherics more than anything on a movie track. That would mean a 3-channel amp might suit your needs, but those amps are a little more rare on this site than the 5-channel variety, and you'll be able to sell the 5-channel amp more easily, I think, if you don't like it. If it were me I'd go with a 5-channel amp, because I don't like the idea of the power coming from two different sources in the rack.
Regarding brands, research Parasound, Anthem, Emotiva, Proceed, and Outlaw, don't just go to Rotel. I've been there are better sound is available for not too much more $$$. Also consider the availability of local service in your area, if possible. I try to only buy used gear that can be serviced locally. Amps are fairly simple to work on, but still I'd make a few calls.
Regarding brands, research Parasound, Anthem, Emotiva, Proceed, and Outlaw, don't just go to Rotel. I've been there are better sound is available for not too much more $$$. Also consider the availability of local service in your area, if possible. I try to only buy used gear that can be serviced locally. Amps are fairly simple to work on, but still I'd make a few calls.