I already have a 70 watt sony subwoofer and 2x120 watt speaker stacks for left and right. My current receiver doesnt have enough watts to support additional speakers. I'm trying to figure out what receiver/additional speakers i should get in order to set up a 7.1 surround setup while still using the speakers i currently have. The speaker stacks in particular were left to me by an uncle that passed and i'd like to continue using them for sentimental reasons.
If your current AVR is 7.1 but just can't power the stacks you can add a stereo power amp to drive them. If the receiver doesn't have front preamp outputs you can use a speaker to line level converter to connect the amp to the front speaker terminal.
If your AVR isn't 7.1 you will need a new one. Power specs on AVRs are meant to exaggerate the actual amount of power they produce so you might need to spend more to get one that will power the stacks you inherited. An AVR rated at 100 watts might produce as little as 30-40 watts per channel under normal use. Very deceptive.