I'm no expert but when I had my son bring over my new SVS SB1000 to install after "breaking it in" for me (he wants one BAD now for himself), I had the same question as the SB1000 has the same sockets. He said the red is for the right channel if both are used as straight line-level inputs, though internally combined for output. A single LFE output from a receiver or amp is a signal already combined, it seems.
Of course my son could easily be FOS.
![Roll Eyes :rolleyes: :rolleyes:](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)