I can't even begin to understand all the terms and conditions listed in the EULA, so I just formed my own opinion based on all the rules originally laid out by Microsoft when the free upgrade first started. Some of it has disappeared, been taken down, rewritten etc. And it's open to interpretation. Lots of people have a very different interpretation of those rules, and I respect that. That's why I don't debate it anymore. It's a no win conversation at best, IMHO.
For the old tuner card being far more problematic the solution was finding out the exact chipset used on the old PCI card was then put to use on a newer PCIe version while the software changed a bit from the old Legacy/XP gui to a newer Media Center appproach. When 10 instantly found the 8.1 driver I still needed a working app and gave the new card's MC approach the test and found that went wel.
For the sound card the 8.1 driver set wasn't neglected by the 10 WU either while sound card's software portion had to be looked up for the 8.1 flavor which then sees the web updater run following the system restart required for the 10 update you still can't find at the support site anywhere. Creative is simply too busy pushing newer models out to be bothered and lets the web updater do the work.
Only one gotcha: If it's an OEM that came with Home on it and you've upgraded it to Pro, you may have to jump through a few hoops to get back to Pro.
If the above applies, go to this thread and read the first post. Installation and Activation of Windows 10 Pro - Windows 10 Forums
I don't know if there's a tutorial on this issue yet.
However, that said, through all the testing we've all been doing, there is more than one way to skin this OS, but . . . new info says maybe not for too much longer . . .
Did I give the impression that the Digital License would be lost by going back to the original OS, or are you being sure the OP knows that it won't be lost? I truly don't want to give wrong info.