Proper Gain Staging

What is your technique for getting the correct mix of gain/volume staging with the KPA (and other gear, namely audio interface)? I haven't tested the SPDIF out yet (see that 1.04 is out so will upgrade first, then test). Here is where I am at, just wondering if others are similar:
Monitor Out volume = -10 (I play at very low volumes, even through power amp + cab and my power amp is an EHX Magnum which can get LOUD fast so that is also set very low. Sounds good.
Headphone Out volume = -12 This headphone setup kicks ass, best I've heard in a modeler and surprisingly inspirational to play through (which NEVER happens using a modeler). But it's HOT, very loud so I keep it at -12 and it's working
INPUT SENSE = my IN SENSE is always clean because I'm not using any pedals in front (is this the criteria for this setting?). I found I had to drop mine down a bit (can't remember exact number) for both my Strat and LP because I was seeing the Master LED go into RED too often and I was hearing some unwanted digital distortion (although overall the breakup tones on clean sounds were very pleasing!)
MASTER = I'm keeping this around -6; anything above this sounds AMAZING but it seems to clip my audio interface LINE INS (Focusrite Scarlett 18i6) and I also see the MASTER LED touch orange/red. Am I paying too much attention to the MASTER LED???

I'm trying to build my rigs and also match their volumes to one another. I see that some user imported profiles are super loud (those Carvin Legacy's are crazy loud, but fun!) while others are much low (Fuchs Blackjack 21). I'm trying to be slightly louder than the default profiles, but I am keeping them close in volume as my baseline -- I think there are some GREAT built in profiles!
But on some of the profiles I am tweaking the "Volume" control is not giving me enough or it's changing the color of the profile too much. I'm doing a lot of balancing of GAIN / VOLUME. I noticed Guitarnet70 mentioned using the Volume control in the cab section? What exactly does this do? Is this the fix to use to get more volume out of low volume profiles? Does it effect the profiles tone much?
I KEEP FORGETTING to sign up my serial number on the main Kemper site, I promise I will do that tonight so I can start posting the in right places.

Quote from guitarnet70

In my feel the amp volume saturates the output very quickly. If you use the cab volume that doesn't happen. It does not change the tone either.

Cool, I have to try this when I get home (after the kids are asleep of course). Thanks!

Quote from XpennoKPA

Ok, I'm confused. Can someone confirm or deny the following

Raised to the volume in the Amp section does not alter the tone, it just makes it louder.

Using just my ears and eyes I find that the VOLUME control has a pretty small sweep (meaning you really have to crank it up to get the volume to change much). This also seems to impart a little coloration in the overall tone, but that might just be my perception. On the flipside incrementing the cab volume by a few points seems to add just enough to balance volumes and I don't really hear much change in overall tone at all.
I usually balance across both the get where I want to go.