To the right of the LFE RCA connector are two RCA connectors, plug a functioning cable into either of the RCA inputs.
As to the LFE RCA input, you're going need to fashion an extractor. The easiest way is to lightly punch the broken tip, deeper into the RCA connector and then with a fresh drill that matches the shaft opening, drill the tip out.
The alternative is to use a fine bit, drill a center hole and use an easy out extractor which is a reverse thread removal tool. In my opinion, no matter what window you open, you're going have to do a bit of surgery to repair the problem. In the interim, you can do what I suggest and use one of the "Line Level In" RCA connectors.
(you do not need to connect to both Line Level In RCA connectors)