in low volume mode I think the FX loop is active, as the point of LVM is that it's the same as the high vol mode except it's quieter and also uses full DSP amp models to give you that cranked amp sound at low volume.

not sure off the top of my head about FX loop being off when in standby.  I think in standby the direct out is all DSP, as there's no power to the power tubes in standby, so I imagine the loop wouldn't work, but I've never tried that as I've never needed to know.

Hope that answers half your question

Rowbi