I think the A85U is the same as the Gibson one ?? I get plenty of gain from the garphic equaliser so that's not a problem. Just concerned that even with the controls set flat the box is colouring the sound from the guitar before hitting the (valve) amp.
And another thing.................when using the internal transformer to output Hi Z, both the treble and bass controls act as volume controls. Either is capable of reducing the volume to almost zero. This does not happen in Low Z mode. Does this happen with the real Gibson ones ??