There are several factors at work here.
Firstly you may just be used to modellers and their sounds. Most modelers really hype up treble and bass and suck the mids, this gives you a very exciting and punchy tone, but it's also nothing like a real amp (without some studio magic). If that's the situation for you then your best bet is to slap a Studio EQ effect in the X slot of your profiles, then use this to boost your treble and bass and diall down the mids.
The next issue may be that your unit may need to be properly set up, first task on that way is to do a System Reset, this is dont simply by holding down the System button while you boot up until it tells you it's doing a System start. This sometimes clears settings on the output channels that may be affecting things.
After that you should look at your input and output settings. Unless you have beautiful studio monitors then chances are you will need to adjust the output EQ to counterbalance the natural tone curve of your output system, if your speakers are naturally muddy then you will need to reduce the mids and bass a little and possibly push the treble very so slightly. I don't know anything about your Tannoy speakers, but if they emulate an amp cab then you may even want to disable cabinets on the Kemper and let them do their job.
On the input side you're going to want to adjust that noise gate, probably all the way to off (my personal preference), and then adjust your Input Clean and Distortino Sens settings until the amps start to feel "right" and react as they should.
Next you may want to adjust your amps to be brighter if your guitar has particularly dark pickups. You can do this with the usual amp EQ settings, particularly the Presence control, but also in the cabinet settings and in the Amp itself by manipulating the Clarity and Definition controls. This is an area that's well worth exploring to begin with. Once you have somethigns et up how you want then just store the preset.
Finally different Cabinets may prove better for some folk. Many people seem to get a sound much closer to what they were personally after by changing out the cabs using Tills cabinets, they're not for everyone, but they might suit you down to the ground, so they're definitely worth checking out at the very least.
Bear in mind that the Mr Nice Guy patch is a very strongly effected patch which to me sounds much more like an old school sim, this may just be more what you're after. In which case your first port of call is going to be compression and after that some modulation and delay/verb. The kinds of amps you'll want to work with are Mesa's as they have a very smooth gain structure, and you should tryt hem out with one of Till's Recto cabs. Working with the KPA is more like working with real amps, warts and all.