I have an old Polytone amp in my garage with no speaker - 12" model. I know the amp works, I just never got around to buying a replacement. I now have a Shuttle 3.0-10. I was wondering if I put a speaker in and wired it parallel to the extension speaker jack, would it work as an extension speaker for the shuttle too? What kind of rating speaker would I need to handle the 300w at 4 ohms?