There is a storage area in the terminal where you can pay a few dollars to have your baggage kept. For that matter, if you explain the situation at the Delta baggage claim office they just might allow you to keep it there for free.

I do not, however, know if you will be allowed to park your car outside of the terminal long enough for you to go back inside and get it.

Frankly, in your place, I would not trust Delta with the keyboard. If the price is at all reasonable, I would suggest giving it to Fedex and having them deliver it to your final destination.