Alright thank you guys. I think i'm going to purchase a powered subwoofer. One more question - a lot of the ones I've looked at have an RCA line in with L/R (like this: https://m.media-amazon.com/images/S/aplus-media/sota/04898c4d-43e8-471e-b4c1-03540d49461a.jpg)
The sub out comes as one jack...
The kit is an old philips 5.1 system, the speakers all work fine. The receiver was starting to have problems, so we purchased a replacement stand alone receiver from Denon (https://tinyurl.com/y7g87qzt). The old receiver had the sub amp built in, and this one does not appear to (the sub output...