Ron,
I meant to say that on the dgx670 you can set a mode in "utility" where the internal speakers can be left on or off when you insert your stereo jack in the back to go to external sound systems. In the DGX660 if you did this, you would have to go to an edit screen and turn the feature on or off but on the DGX670, once you set this it will remain when you power off and turn on again. This was a big improvement. In my store if I left the jack in and someone turned the keyboard off and then on again, it would always be in headphone mode and you would here nothing if you didn't have the external amp turned on. Now, it's no longer a problem. I hope this makes sense!