Sharing a subwoofer with 2CH and HTs rigs!

Some (All ?) REL Subs have stereo inputs and a separate LFE .1 input and each input has its own trim.  

Thanks. I have an older Velodyne that has line level/LFE and speaker inputs with one dial for crossover level and one for sub volume, but I’m not worried about which input on the sub (I need to live with the RCA inputs if I’m gonna use two amps as separate inputs). Just trying to figure out if the switch box is an effective tool to split two amp signals into the subwoofer. Worried about sound degradation or it being a problem somehow for the sub or amps...
Is this the way to do it? Or are there other options?

I use my JL E112s for both home theater and music. The inputs are summed. So you can send the preamp to one input and the reciver lower frequency output to the others. This still lets you high pass the mains and play the receiver’s out at the same time. I have been doing this for years without issue. 

In the velodyne manual it expressly IN ALL CAPITAL LETTERS AND BOLD says do NOT use both low and high level inputs concurrently... 😕

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.