I use a Behringer Ultra-G 100. Speaker cable in>Speaker cable out to cab>XLR out (cab sim off) into the Capture port on the QC. Very pleased with the results. Add a Cab or IR and you have the magic sauce.
I uploaded a few D50 (Dumble 183 clone) captures using this. Try them out. I use the Zilla H75 (16) cab with a 57 and 421.