We tried to do a fairer test by making sure all effects were removed and we recorded headphone vs SPDIF again.
But we noticed there wasn't much difference again with all effects removed.
But headphones through Kemper STILL sound great.
HEADSCRATCH
We had a hunch.
Lets bypass focusrite and record headphone output through the computer mic.
We played back through headphones on computer (NOT Focusrite).
Now we're getting tones like the kemper headphone output.
We then listened to the other samples we had done on computer headphone output and Focusrite headphone output.
So conclusion:-
The headphone output of the Focusrite Scarlett 18i8 sounds like SHIT.
I always thought of Focusrite as flagship when it comes to audio devices (used throughout the world in studios etc) (250 quid - Ok you can pay much more but the computer headphone output sounds better)
So this conclusion has astounded us.
Obviously the mix of the track I uploaded as an example clearly isn't up to scratch as we're mixing via monitors and headphones through the focusrite.
So no issues with Kemper, Cables or Cubase.
Thanks to all who have contributed.
We'll try and post a track when we are happy with the mix and sound.
We'll also remember to listen via Kemper when sampling new profiles from now on.