IMHO a good low gain profile is just as hard to profile as a good clean sound. It's all about harmonics and dynamics. Every profile I do, is tested with both humbucker and single coil on both neck and bridge pickup. This helps me to get the balance of the profile right.
Single coil bridge pickup tend to sound a bit glassy on the Kemper. I keep on moving the mics untill that is just gone. Still you need enough high frequencies to keep the sound alive.
One of the Princeton clean profiles (Series 4 I think) is often used by Dutch professional player Angelo de Rijke. This is a special series to me. I used the Heil PR-40 on that series. This is a dynamic mic with almost condenser qualities. The result is a very dynamic and detailed series of profiles. But maybe you like other series better. All the Princeton series are really good. I liked the amp so much that I made 5 series, where I usually make only 3.
The Vibrolux has nice cleans too. It is a different amp. It sounds bigger (which is also is;) ). As I recall, the Princeton still had its original caps, whereas the Vibrolux was recapped. It changes the sound. Personally I prefer the Princeton, but would also be very happy to play the Vibrolux profiles on stage 
Listening to the demo's may help. Unfortunately I can't publish lossless demo's, so the profiles will have more sparkle and dynamics than the demo's.
I hope this helps.