As one struggling to get a Sony DRU820A to first recognize dual layer media and then burn it…I consulted Sony’s media compatibility document

This document indicates Sony does -not- support their -own- dual layer media for a DRU-820A? This is a bit surprising! Note the date on the document is October 13, 2006.

Coulda sworn I checked their compatility prior to that and Sony DVD+R DL WAS supported. Have they backed off? Am I missing something obvious?

That drive is actually a Benq 1670 rebadged by Sony IIRC. Sony DL media has been reported as being made by Verbatim or Ritek. Sounds like you have the Ritek made as the Verbatim is the most widely DL media, mainly for reliability compared to the other choices.

You could update the firmware if you haven’t already and see if that helps.

I used some Sony made Sony CD-R media on my Liteon made Sony CD-RW drive. Not the most brilliant combination… (or maybe it just was poor CD-R quality :). I guess there are no guarantees of this sort.