The first time this happened to me I had not disabled the kms drivers. I only disabled them when everything started failing and I was never able to fix it again (had to roll back to a backup).

Thanks as always for the swift response.

@moltke44 You can try any command you see fit, but the package will not work under Jessie - even if you get it installed.
As for the update to Stretch, the recommended method is to use a new image from scratch and transfer your configs/roms/etc. to the new image. It's possible - technically - to upgrade in place, but as you already found, it's not always optimal and you can end up re-imaging anyway.
Remember to backup your image before attempting the upgrade - with any method you choose.