Correct me if I´m wrong, but I was told that the upgrade involves the installment of an Air module into your old D4 pack. This would give you full control over the pack through an Air Remote receiver/transmitter or an Air USB transceiver connected to your computer just like the new version of this pack. I would definitely have invested in this upgrade have I kept my D4 packs. But after careful consideration, I decided to invest in the new 8A system after all, just not to the extent that I had originally planned to do.
Best, Per Bernal