loosing discount

You would still have to have your debit or checking account as your default payment in your account and setup with autopay.  Whether or not it allows you to still get the autopay discount by paying early with your credit card, I don't know because it doesn't take effect on my account until the next billing cycle. 

I would assume that paying with a credit card, even if paying early with a debit or checking account as the default payment would automatically remove the discount.