For a great high gain lead tone, use the UK80's or UK MDN amp models (a Marshall JCM800 and a Marshall JCM2000) and crank the gain, set the bass and treble to taste (preferable over 50%) and make sure the mids are set anywhere over 60%. Should make for a fat lead tone. If you're using single coil pickups you might have to set the bass a bit higher for a thicker tone and if you're using humbuckers you might want to lift the treble for a bit more cut.
You could use a little bit of COMP (maybe 30 - 40%) from the PRE FX section to add some sustain to the tone. I would also use a small amount of the ECHO+ from the DELAY/ REV section to add some ambiance and space to the tone.
Also you might want to adjust the built in noise reduction down a little as it tends to rob a bit of sustain. You might add a little noise to the signal, but it does help the tone. You can adjust it in the LEVEL/ NR/ CAB/ PEDAL section.
Personally I hardly touched the presets. It's far better to experiment with the different amp models and the settings to find a decent tone. I liked the Marshall (all the UK amp models) and the VOX AC30 amp models.
If you don't have the manual for it, you can download it here:
http://www.korg.com/uploads/Support/AX5G_OM_EFG2_633661622631280000.pdf
Hope that helps. ?
