Sharing a subwoofer with 2CH and HTs rigs!

Flynnrd, I understand. 

Using the SYS, my thinking is that you could run a pair of RCAs to  input 1 from one amp and to input 2 from the other. Then run a pair of RCAs to the sub from the SYS output (or a y splitter to a single RCA if the sub has single input). Being very careful about having only a single amp on at a time, having both turned off when switching which to use.

I believe the same could be said for a switch box. 

I hope others will chime in on possible problem with use of a switch box. I would think any quality one completely isolates inputs. I doubt one would want one's sub to receive signal from two preamp outputs at the same time.

The issue differs between use while both amps on and use for selecting which audio vs. video amplifier to have on and selecting routing to sub without movement of cables.  Do you really need to have both amplifiers on at the same time. Is warmup a concern?

I am also interested in what others contribute.