I have an old sansui au 717. I think it is rated at 80 wpc, not sure don't have paperwork. I am looking fer a good set of speakers fer it and am confused as to how Polk rates amp power for speakers. Lets face it, a range of 20-300 watts is a big spread. I would like to try the rti7 but don't know if my amp is up to it. What guide lines sould I be a looking for in looking over the choices ???