I would plug Kabinet into the poweramp, Send Main Outs to PA/FOH. And drink a beer on an empty stomach. 
As Bayou said, plug your cab into the Red Speaker Out with a speaker cable.
let the sound guy take either one or two XLR from Main Output straight to the. FOH desk. Already, line level balanced signal so ne need for DI boxes although some sound guys will still prefer to use them.
If running only one cable to the FOH make sure to go into the Output Menu and select Master Mono for both Main Output and Monitor Output. If you don’t you will lose half your signal as the KPA doesn’t automatically sum a single stereo connection to mono. (E.g. if you have a sound with ping pong delay you will only get ping OR pong as the other will be going to a silent output)
Also in Output Menu unlink the Master Volume but make sure Monitor Volume is linked. This will let you use the Master Volume knob on the front of the KPA to control your stage volume without affecting the signal going to FOH.
Also, tick the -12db box to avoid sending too hot a signal to FOH.
Make sure Power Amp is turned on and set powere amp boost to a healthy level like +6db (you can always tame it with the master volume if required but if it is too quiet you are stuck -the Kemper doesn’t go to 11.
You might also want to save these settings as an Output Preset so that you can always return to them in future.
Although it is tempting to want to set up hundreds of different rigs and performances to make the most of all the options available, keep it simple until you are really comfortable with it. A single performance with 2 or 3 rigs loaded and maybe some Stomps/FX just like your old tube amps will make it feel more natural and let you concentrate on playing instead of worrying about your rigs.
have a great gig ?
...
Although it is tempting to want to set up hundreds of different rigs and performances to make the most of all the options available, keep it simple until you are really comfortable with it. A single performance with 2 or 3 rigs loaded and maybe some Stomps/FX just like your old tube amps will make it feel more natural and let you concentrate on playing instead of worrying about your rigs.
...
I like that tip. 
Hey all, I have the powered toaster, remote, and Kabinet. I have my first live show Saturday after playing tube amps for years. Anyone got any tips?
I want to essentially run the Kabinet as a stage monitor along with other monitors. Do I just plug the kab into the Kemper at the same spot? And where do I tell my sound guy to plug in for DI?
Any other tips would be appreciated. Thanks!!
Honestly, with your quite basic questions it seems like you didn't spend a lot of time with your (new) setup.
And I fear you bring yourself into some stressful or unpleasant situation if you have no time to try out everything in a rehearsal or 2.
Like find out where to plug everything, including speaker and FOH feed. Like finding where in the menu you can separately change the master volume for FOH and you Kabinet. (You might want to change the level for the cabinet more often so its good idea to assign it to the Master Volume poti on the Kemper).
Also find some sounds that work in your rehearsals, that work with your arrangements and that work in the bandcontext AND are fun to play.
All is said by Wheresthedug as often
On the other hand, i rejoin Tenderboy's advice.
I do some photography and it reminds me an advice i was given ; don't buy a new camera just before a trip....
My top tips are basically the same:
1) Make sure you have the -12db ticked to avoid frying the desk or reduce your output volume
2) Unlink your volumes, so you can control your on stage with no impact to the desk feed
3) Sort as much as you can at home prior and be clear on the main settings. So be ready for the xlr lead from the engineer so you know where you are plugging in and its already set to master mono. Play with switching your sounds, make sure they are balanced etc.
4) Sort the FOH sound first and check engineer is happy. He can feed you monitor signal worst case. Then sort your on stage.
5) Allow a bit more set up time. Tell the engineer its a new set up and that you'd like to plug in early to check everything.
Its probably too late now but I would also have auditioned the sounds via an FRFR speaker at volume as the sound from your Kabinet will be different.
In general though, its relatively straight forward. As long as you get a good sound, then you can tweak later. Don't let a new set up stress you out or ruin the show.
One of my first times out, it sounded different to what I thought it was in my head. I stressed the whole gig, only to be told by the engineer what a great sound I had, so I had stressed myself out for nothing - no-one ever told me that when I had my valve amp!!! Also unless your sound is dreadful, no one will really know, but they will know if you are stressed i.e. keep it in context!
Oh, one other thing - ROCK OUT!!!!!
One of my first times out, it sounded different to what I thought it was in my head. I stressed the whole gig, only to be told by the engineer what a great sound I had, so I had stressed myself out for nothing - no-one ever told me that when I had my valve amp!!
I had exactly the same experience. I thought my sound was a bit shit but just got on with it anyway. After the shoe the FOH and monitor engineers told me it was one of (if not the) best sound they had ever had. ???
congratulations on the show ?
