I've listened to many demos of Korgs nylon/concert guitar sounds. To me they are all too treble sounding. Is there a way to make the sound deeper and fuller like Yamahas nylon/concert guitar sounds by tweaking it? Anyone who have owned recent korg and Yamaha models should know what I'm saying..or is it just bad audio on demos?

There are some great ones in there, but not necessarily the ones that come up on factory keysets (OTS). And, any of them can be easily edited.

Try looking in legacy and gm sounds. There are so may to choose from as well as normal factory sounds. Click any sound you have up in a style and there you will find all the sounds.
MEL

Let's be honest when it comes to Guitars Yamaha is King of the hill....

Agreed.
One main reason I stick with Yamaha ...
Eric

I actually like a lot of the Korg guitars a lot, not taking anything at all from the Yammies.
Sometimes with the Yamaha guitars, I find myself taking off the automatic articulation so the guitar will do more what I want it to do when I play the keys. The Korg DNC is often more subtle, but it's really all a matter of taste.
I do really like the Pedal Steel on the Yamahas.
The guitars on both can be deeply edited, with e.q., amp sims, etc. But I don't do much of that because I'd rather just play.

I use the nylon guitar and slide nylon guitar a lot and that is what I am really looking for, to see if Korgs can be made to sound like them. The nylons on my T2 are excellent.

Don’t be coy Don...you made those 970 🎸 guitars sing.

jingleman

No, I was saying the Yammies are very good; not trying to distract from them.
Korg's are very good too.