Apologies if this has been mentioned already (still reading through), but over-enthusiastic palm muting can cause boomy bass sounds in the background. Lighter touch required.
EDIT: OK I've caught up and it appears to be a general amp characteristic that the Kemper is reproducing accurately. So why does it not appear in more commercial recordings? What is the recording engineer doing to dial it out?
If you have followed the thread, it's now obvious that you cannot really "dial it out" after it's recorded.
Schreckmusic had to carefully set the gain and amp volume to find a spot where it doesn't produce "windtunnel" noise on hard hits.