Multiple inputs to Velodyne DD DD-18 sub?

Hi,

I am working on putting together a separate home theater system in the same room as my 2-channel. My plan was to share the Velodyne DD-18

The DD-18 has three inputs:

Stereo RCA (what I am using for 2-channel)
XLR LFE line-level
Speaker level stereo

The local Velodyne dealer claims that I can use on ONE of the three. That doesn't make sense to me. I don't set the input - the DD-18 just senses it when a signal is present. It would seem that as long as only one is providing an input at a given time, it would be fine to use two inputs.

Does anyone have experience with this?

Thanks,

Jerry