I remember someone posting on HTF a while ago who tried this using Y splitters. (Well, in this case, "combiners" ! )

That person posted that the input level was way reduced when she/he had both inputs occupied vs just one. Sounded like he was changing the input impedance the pre/pro input was seeing.

Maybe it was specific to that setup, but something to watch for...

In essence, having that level reduced, and then having to compensate by raising the volume, you might end getting a higher noise floor along with the goodness of pure analog!