Hi everybody,
sorry for answering that late but it took some time testing around with some configurations.
But finally here are my results.
I tried Tim's suggestion backing off the panning a few clicks but it doesn't work in this case.
In fact, regardless to the degree of distortion or gain the signal of tone 2 is processed with, with the setup I mentioned above everytime there is this cross modulation to the aux in. It's just that the higher the gain or distortion of tone 2 the more it gets amplified and therefore audible.
But while testing other configurations I found out something interesting.
This time I routed the aux in channel to the tone 1 processor and the guitar in to the tone 2 processor again with a full panning left and right.
First I thought I solved the problem because it seemed that the cross modulation disappeared meaning I couldn't hear it with a fairly high degree of gain and distortion on both channels.
So I tried to apply the maximum of gain that is possible on this device by adding a stomp effect like the screamer or classic distortion with its full level of gain and distortion and I noticed that the cross modulation is still there only this time logically on the guitar in channel and with a level that is quite inaudible because it is so low that it gets masked by the noise that is produced by the amplifier model itself.
For future recording sessions I'll use this setup and see if I can live with that.
But however it's not the way it should be and it seems obvious that this is a buggy behavior.
I hope that line6 will take this into account and maybe one day this could be solved with a firmware update.
Thanks for listening.
