Hi,
I use the accoustic models with my HD500 as adviced by a line6 endorser.
No amp model, if needed some effects and the last part of the chain is the FX Loop.
I go out the fx-send directly into the FOH.
As there is no fx return, the signal will not pass the normal output and the technician is able to tweak the sound of the accoustic seperate to the normal signals.