EDIT: Before you read the following statements you should know that by now (late February 2021) I disagree with several of the points I used to make here. I still decided to keep the thread because of the interesting replies, not the least by C. Kemper himself.
That I changed my mind on many of these "issues" shows how subjective sounds are but also how much the experience with a Kemper changes over time when one gets to know the little machine a bit better.
I own my Kemper (as well as my Kemper Kabinet and remote) since a little more than a month now and have gone through all five D-A-B-D-A stages by now. After reaching acceptance I thought it would be a good idea to collect some of my thoughts in a "I wish someone had told me earlier" manner. Maybe it can be of help for someone.
Don't hesitate to disagree with me or add your own thoughts. I guarantee it's gonna be 100% subjective anyway.
Here it comes in random order. I might add some more in the future.
1. Turn off "pure cabinet" in the global settings and you'll get closer to the tones you are looking for.
2. Most profiles sound nothing like in the youtube videos that advertise them.
3. Most profiles sound bad "out of the box". Working with the Kemper is all about tweaking.
4. If you (like me) already spent hours with your real amps and pedals in order to find the perfect sound, you'll spend even more time turning knobs on the Kemper. The Kemper almost guarantees that you can find the tones you're looking for but it takes even more time than the analogue way. I was wrong when I thought the Kemper lets me focus more on the music than the chase for tone.
5. Start limiting yourself to a handful of profiles as early as possible or you'll never start making music.
6. The profiles you'll like the most might not be of the amps you like the most. I love Supro amps and have yet to find a Supro profile that sounds amazing with my guitars. There's too may parameters that make a good profile, and the source amp is only one of them.
7. Don't listen to everyone telling you that adjusting definition is all you need to do in order to figure out if a profile works for you or not. In my case boosting bass and treble often gets me closer to a good sound than definition.
8. Many professional profiles seem to be set up for very low output guitars. If a profile sounds too boomy it often helps to reduce the gain. One of my main guitars has a higher output gold foil pickup and I need to reduce gain in 50% of all my profiles to make them work.
9. Recording with SPDIF is a MUST. Investing in an interface with SPDIF input is totally worth it.
10. The Kemper Kabinet probably won't make your profiles sound as if the actual amp was in the room. A 12" speaker will never sound like the 4x10 Fender Bassman or 4x12 Fender stack you're looking for.
11. The Kemper Kabinet does not make a good monitor speaker. (Please convince me that I'm wrong.) Using the Aux to feed in a backing track doesn't sound very convincing to me.
12. Shapers are underestimated and often get you the sound you're searching for in the distortion section.
13. You can stop trying: the Kemper remote doesn't let you morph from one profile into another one. You can't morph your favorite Amp X clean profile (i.e. Fender Deluxe 2) into a gainier version from the same set (i.e. Fender Deluxe 5).
14. Adding gain to your favorite clean profile rarely turns it into a great crunchy or distorted profile. Use a different version of the profile or pedals instead. (This was my biggest disappointment since it really stops the Kemper from feeling like a real amp.)
15. The looper in the Kemper remote has an insanely short recording time. Don't sell your boss loopers (like I did...).
16. Paying for profiles is worth it. All of my favorite profiles I purchased.
17. You'll surely have noticed the hype about M Britt's profiles. When I started playing with them I was pretty disappointed at first since they sounded dull and muffled. But after adding treble and some definition many of them actually became my favorites. I'm sure it depends on the guitars you own. To me, Tone Junkie's profiles sound better out of the box and require less tweaking. So spend some time finding a professional profiler whose tone fits your guitars and ears best.
18. The "Space" option in the output section is a very powerful tool to achieve a more natural sounding tone and doesn't need to be limited to headphones only.
19. Equalizers can be your good friends. Before the amp section they can help you shape your guitar into something that works better with the amp. The "cut the mix" EQ after the amp section can make dull profiles sound much better. Tone Junkie has some great youtube tutorials for the use of EQs and offers free downloads as well.
20. You cannot use the Kemper's effect loop and aux in or record a direct signal for reamping at the same time. Although I love the fact that I can use external pedals with the Kemper and place them anywhere in the effect chain (genius!) it's very frustrating not being able to record a direct signal at the same time.
All right, Kemper wolves, come and attack me.