Hello TresorTX
After thinking about the question I came up with a possible solution.
1. Turn all reverb and effects off on both boards and any external equipment. (This will allow you to here the native sounds)
2. Adjust the volume levels so that both keyboards are the same. (Are the Korg sounds still up front?)
3. If the Korg still sounds up front then ask the question why. (Brighter, more bass, midrange etc)
4. Adjust the output EQ on both boards so that the sound characteristics are the same. (If you can’t achieve this then you will have to make the balance as best as you can)
5. You can now start applying reverb and effects etc. (Use an external reverb effects unit or feed the output of one key board into the other so that the same reverb, effects etc are applied to both keyboards)
I hope the above helps, however if you can find a sound engineer, he will probably be able to help you better.
BTW For other uses the combined prices of the above boards work out about the same price as a Wersi Ikarus which is designed to integrate dissimilar instruments (Akai samples, VSTs etc) and with the new Open Art Arranger software can Direct Play Yamaha styles without conversion, (The Ikarus also comes as standard with 80Gb hard disk, DVD/CD Burner combo drive, Floppy Drive, 4 USB 2, more Real Time sliders, 76 notes, large colour touch screen etc) plus you also don’t have to change it every 2 years to get the latest sounds etc. (That’s the beauty of software based instruments)
Anyway enough of the sales talk, and I hope you manage to get your keyboards nicely balanced, as they are both excellent instruments.

Bill