I've managed to solve the issue, but not the way I would have liked.

I ended up buying a copy of Windows 8.1 64-bit and upgrading to that.

This then allowed me to run the DirectX End-User Runtime web installer and run the updates.

I then needed to upgrade my graphics drivers to be compatible with 8.1, then I've been able to play ever since.

I guess I'll never really figure out why I couldn't fix this on Win 7