Under normal conditions(efficient 8ohm speakers, smallish to mid sized room, medium volume levels), the Pioneer SC-25's amp section has more than enough power. With a larger room and low impedence speakers, an outboard amp might be a good option. Keep in mind that the ICEpower amps are very efficient and powerful and adding an amp might change the overall sound of the receiver(good or bad). JMO
http://www.soundadviceblog.com/reviews/pioneer-elite-sc-25-av-receiver-product-of-the-day-8-2010/
Demo it by itself and draw your own conclusion.
Bill