Figured out and solved my problem. My Dell business rep likes when I place my orders through him, but I realized that when I click through his email to pay that's when I'm limited to 2 payments (I'm guessing it's similar or same to price match quote which I've never done, just my assumption) but when I just checkout regular through my shopping cart it allows me to use 3.

Since I get no monetary benefit (such as in the case of a price match), I'm sorry, but I just ditched going through the rep and easily completed the checkout using 3 Biz Plats. I hope my order doesn't get canceled and that I receive my computer and subsequent credits plus 15% cashback in short order.