1. Why do you use the Monitor Out? Try the Main Outputs instead.
2. Share more information on your audio interface, the speakers you use, etc.
I use a focusrite solo interface
That's probably part #1 of the problem. You can only use a mono output from the Kemper Profiler through this audio interface. When you listen through headphones directly connected to the Kemper Profiler, you'll hear glorious stereo (and likely also something called "Space").
have not used my monitors yet,they are maudio bx8 d3s
How about connecting them directly to the Kemper Profiler Main Outputs (without audio interface in between)? At least for a test how the monitors sound to you.
when i running kemper direct into rig manager through pc
That's not possible, you can't run "Kemper into Rig Manager"
if you can recommend a good audio interface that outputs stereo that wont break the bank
Have a look at Focusrite Scarlett 8i6 or Presonus 68c if you're on a budget.
using vsts straight into monitors from interface sounded terrible
1. How does regular recorded music sound? Your favourite bands' records?
2. Make sure you don't place the monitors' backside close to walls, keep them 50cm (20 inches) away from walls!!!
3. Switch the "Acoustic Space" on your monitors to "Flat".
4. Make sure you've setup decent gain-staging. Don't push the monitors' "Volume" knob to max and the computer playback extremely down. Do pretty much the opposite ... a. Volume on monitors ALL the way down ... b. Music playback on your computer up to 0dB ... c. Now up the Volume on your monitors until you reach the maximum loudness you ever want to listen in this room. ... d. Now turn the computer playback volume down to a comfortable value and you're set.
5. Acoustic room treatment!!!!!!!
6. Always remember that you haven't bought the most amazing monitors on this planet. You went for budget monitors (obviously for reasons), so don't expect them to sound the most glorious ever. 
But they should sound MUCH better than any PC speakers nevertheless, of course.
This guy in the video has the monitors wayyyy too close to the wall. These monitors have bass reflex openings in the back, they need space so they can "freely breath".
Just imagine you stick potatoes in your car's exhaust pipes ... it won't run smooth and if you're lucky and the motor stays on, it will lack plenty of power. 
Lightbox is the man on sound treatment but I suspect your issue is pretty basic. I have run my Kemper in mono through my interface and it sounds great so don;t rush out and buy a new one just yet...but it will of course sound less "wide".
I also suspect your monitors are OK, yes lower price but should still give you a reasonable sound.
As said, break it down to ensure a strong signal and the set up so start with direct connection to monitors.
You also didn't explain how you got your glorious sound via rig manager? You cannot get sound via you laptop without an interface. Rig manager is only the way to select a rig and has nothing to do with the interface. Was that through headphones or some other monitoring solution?
I suspect your issue is a combination of things, hence you'll need to take it step by step.
I use a focusrite solo interface and have not used my monitors yet,they are maudio bx8 d3s.
guitarguitar shop told me to use the monitoring output but it really down grades the sound.
on my focusrite solo i have one guitar input and two line outputs.
That's not true about the monitor outputs downgrading the sound. They're the exact same quality as the other outputs, they're just XLR instead of 1/4 inch. FYI, this whole song was recorded via the monitor outputs into a Focusrite Scarlett (8i6 in my case, but should sound identical to a Solo). https://empiresoflight.bandcamp.com/track/malariff
What are your output settings on the Kemper? And do you have Space turned on in the output section, possibly for headphones only?
