I see now that the hard drive replacement question I raised above does appear to be answered in the "Quick Reference Guide" that's posted on Sony's website, which states: "Do not replace or add hard disk drives on the unit." So much for user serviceability.
But fear not! Additional language on page 7 of the Guide infers -- albeit with incredibly roundabout language -- that hard drive repair and replacement can be handled through Sony. On the other hand, however, absolutely no information is provided as to who one would contact to make any such arrangement. In fact, warranty information about the HAP-Z1ES of any kind whatsoever seems to be totally 'missing in action' from the product's page on Sony's website.
I don't know about anyone else, but I find such omissions as these a little troubling particularly given this humdinger that also appears in the Quick Reference Guide: "Due to the nature of the hard disk drive, we do not recommend you store data on the hard disk drive for a long period." How's that for a disclaimer! Kind of reminds me of the drug ads on TV that tell you if you take this drug your arms are gonna fall off and then you'll go blind.