Willy - I think a good 35 watts will easily drive the Rivals for all but the loudest levels in a big room. I think Stereophile measured them to be 98 db sensitive but I also think that can be misleading in & of itself. The watt meter on my Rogers amp displays the average power for both channels combined at any one instant & up really loud w/ a big bass peak demand, the Rivals are drawing about 50 watts or 25 watts / channel. At this volume, many speakers driven hard by realistically priced & sized amps (maybe & arbitrarily less than $20K & 100 lbs.??) are being pushed to their limit & strain to do so. Of course, my categorization is all relative. My investment in my system is absurdly high to many & barely scratches the surface to some others.
The Rivals w/ the Rogers are just strolling along @ almost any volume (although the Rogers operates in full class A so it's not really) & sound great doing so but you get the point. I almost bought a Prima Luna but once I found the Rogers, talked to Roger @ great length & demo'ed it in my home, I was completely sold. That said, the Prima Luna will probably also sound excellent w/ the any Volti speaker.