Lsi 9 & 7's

I have just purchased the Awesome LSI9'S to go with my LSIC Center Channel speaker and just previously bought a YAMAHA 5760 A/V Receiver. Though the receiver is rated at 110 Watts per channel at 8 Ohms yamaha recommends only one set of 4 Ohm speakers in which the LSI Series is. I was thinking of getting a separate power Amp to assist in my enjoyment of these Great speakers in which i know they will need but a little late in finding out. I have had alot of Stereo equipment over the years to include a mint set of Polk SDA-CRS and Monitor 10B'S in my closet that i will never sell but an Amp is something i have never owned and don't know where to start. By reading i believe you attach one to the receiver using the pre-outs in which the Yamaha has. I guess then the Receiver controls the volume and the attached speakers on the amp???..If someone could help out please inform me. You guys are incredibly knowledgeable here on these forums. Thanks!