roland Dimension D inputs

[Dimitree]

I'd like to understand how the input on the Roland Dimension D works.
It seems that when 1/4" jacks are used, the fet Q110 changes the gain on the opamp after the preamplifier. Why?
Also, I'm wondering if it is possible to replace the XLR + 1/4" jack with a single TRS 1/4" jack, on the output too. Would that still work when using a unbalanced signal (so that the one of the phases is grounded)?

schematic

I've read here:
http://jhaible.com/legacy/subtle_chorus/jh_subtle_chorus.html
the following: "XLRs are not floating balanced outputs - do not connect to unbalanced inputs!"
what that does mean?

[Fender3D]

You got jack on output... just connect your amp there
Since they are not floating balanced outputs you should not connect any unbalanced connector shorting the unused phase, looking at schematic there's no protection on outputs.

I think they lower gain because jack input should be line level.