After 18 months of ownership and a lot of frustration I finally have what everyone is hearing from their Kemper.
I'd tried everything I could think of and was looking at other gear in my chain, guitars, cables you name it I tried it,
I could kick myself now as the first rule of diagnosing any 'computer' is return to factory state. The most obvious thing and I didn't do it. Anyway did the soft button 1 reset on boot and Jeez the difference. My single coiled gtrs which were always the biggest problem/disappointment actually sing, not the brittle sounding tone which would sound like it was split in two with some digital artifact beneath the main note. Each note is now a 'unit' and I can now hear the subtle and not so subtle difference between the amps profiled.
I can play hard on chords and it "feels" like I'm playing through an amp without the middle frequencies masking the top and bottom, its sheer joy - I could cry at the relief
I don't know what was futz in the original system state and frankly now I don't care I'm just happy that my issue is finally sorted.