Adjust the Kemper. The Headrush/Alto are very,very flat, in a good and reliable way. If the results are boomy (and they probably will be) then read the manual about tweaking definition or low shift instead of bass. Here’s what Michael Britt suggests:
Tweaking – Feel free to tweak these profiles to fit what you want to hear just as you would a traditional amp. I strive to keep my EQ section as flat as possible so it gives the user plenty of room to adjust as necessary. I find the Definition control extremely useful in dialing in profiles as it can sweep the focus of the overall eq without having to grab the eq knobs. I often start there. If you find the profile “dull”, start by turning up the Definition. If you find it harsh, try turning the Definition down til it smooths out. For single coil strat pickups, I generally like the Definition between 4-5, for Teles around 5, for P90s between 5-6, and humbuckers between 6-7 as a starting place, but don’t feel limited to those settings. The Power Sagging, Compressor, Clarity control and the speaker Character control can all be helpful as well. Some profiles may require more tweaking than others in getting “your” sound out them. You can also tweak the Low Shift and High Shift in the Cabinet parameters if you find a profile that is too tubby or too lacking in low end.