You don’t need an attenuator. Just DONT connect you powered QSC to the SPEAKER out (red ring)of the Profiler. Use monitor and direct out and just turn the volume down. The Kemper and QSC amps are clean linear amps not like valve power amps which sound different when turned down. Stop over complicating simple stuff.
Agreed to your last.statement. The powered kemper with the red ring is a powered 600w mono output. It is used for driving kemper unpowered FRFR cabinets and traditional guitar speaker cabs, often used with DI profiles, but not always. Me personally i strongly dislike the sound of FRFR no matter what the brand is, to me they are sterile and lifeless. I run mine with 12 inch guitar speaker cabinet, hopefully soon i will get the mod done that will allow me to run stereo, by British audio. If you have powered cabs/ pa monitors; use the directive above listed in pictures.