Evidently, the cart is too dumb to give you the maximum discount. Maybe this will be resolved, but I suspect this will happen after the 25% expires. I suggest that you place your order with the phone staff if possible. Another workaround might be to purchase through a proxy who does not own any SONOS.

Thanks buzz. I did end up using the proxy method and it worked out fine. 

You can remove the  upgrade discount  by hitting the minus sign and it will then revert to the sale discount.

Thanks you, Danny. A little too late, but will be useful for the next time.