Bryan, although you say that both the RCA input and output connectors have come loose, you don't indicate if the output connector can still work. The input and output form an internal "Y", and the output leg(if not similarly damaged)serves equally well as an input. If you haven't tried this, do so.
If this doesn't work, purchase the RCA to XLR plug cable. This shouldn't run more than $5-$10 from a source such as Monoprice. There's no "conversion" that takes place; it simply allows the unbalanced output from the receiver to be fed into the sub XLR input and to operate normally in the unbalanced mode.
