If you're talking about grounded vs. ungrounded (speaker) wire, you need to use grounded wire between an instrument and the amp. No harm to anything if you do-just a lot of unacceptable noise.
Using grounded wire between a powerful amp and speakers can sometimes cause excessive heat and damage.
BTW I still have and use two MS-60's-your keyboard, plus speakers.
R.
[This message has been edited by captain Russ (edited 11-04-2010).]