according to the SOny store, thery have the following specs:
Speaker
* Frequency Response : 40 - 50,000 Hz
* Impedance : 8 Ohms
* Mid Range Size(s) : 3 ¼ " (8 cm)
* Power Requirements : 180W
* Quantity (Packaged) : 2
* Quantity of Tweeters : 1
* Quantity of Woofer(s) : 2
* Sensitivity : 89 dB
* Speaker Terminal Type : Binding Post
* Tweeter Size : 1" (2.5 cm)
* Woofer Size(s) : 6 1/2" (16cm) x 2
According to their specs, they have an in room senstivity of 89db and a nominal impedance around 8ohms. Based on the driver configuration, I would drop that to around 6 ohms nominal or average. Anything lower mid level from Yamaha, Denon, Marantz, etc will easily drive these speakers very loud without danger of over driving the receiver's amps into clipping.