The Opus line are 6ohm speakers and may dip below that. How big is your room? Do you listen at loud level? I used a Pioneer 72txv (130wpc) with my Wharfedales for a while and then added the MPS-1. The speakers definately came alive with the external amp. What other features are important; HDMI, upscaling, multizone?
Is this 2-channel or HT?