To answer the OP regarding whether the 1/4" Amp Outs on my 11R are clean - Yes, totally clean.
In thinking about it, what I would have done next is taken the signal out of the front jack and ran it to a mixer then line level out to PA amp to speakers or my Alesis actives. You can't really know what's coming out of the front by assuming the problem isn't related to a guitar amp - you have to run the signal to something known to be clean.
But I suppose it's a moot point because you already returned the 11R?
And OP, these guys are going out of their way to try and help a fellow guitarist.
Hopefully you'll get it sorted out.