I think the reason why regular store bought gizmos won’t let you decrypt it is because content can require HDCP to make sure you don’t gain access to the data. If there were a device at Best Buy that just bypassed this, I think the DMCA and rights holders would come down hard on the seller.

I’ve heard of gizmos from shadier places may be able to decrypt the data but it’s likely because they’re acting outside of the law.