The mapping is defined by the tuner module which is an official (if unavailable) SB product.

The Sony RM-X4S is what SB says the tuner is designed to work with. Following your logic the FAQ wouldn't address adding third party hard drives.

Sure, its on the CD. Did you know it ws there? Does the FAQ only document things which are documented nowhere else?

Some of the responses (or lack there of) were not obvious. And what is this doing on the riocar.org site?

Now if you want to argue that it isn't a frequent question I might agree with you.