That's a very nice combination. I use a Fender Hot Rod Deluxe which is the 40 watt version of the DeVille. They are exeptional guitar amps and I have have had Fender Twins and Marshalls some years ago and I do know tube amps. It sounds like all you want to do is send a signal either to the main input or to the VG88 through the effect return. I guess you have tried using the A/B box to switch your guitar between those 2 inputs. Do you even need to use the Y cable with the A/B box ?