I'm new to the Kemper scene. I have the powered rack. I would like to use a standard marshall cab for certain situations. I'm using 2 P.A. cabs at the moment through a Carvin TS-100 tube power amp. This sounds very good but, I would like to use a Marshall 4X12 profile at times. My question is/are; Are the FRFR speakers available as replacement speakers for a Marshall cab? Does the cab have anything to do with the flat response of the tone?