1. I used the two external drives exclusively with OPPO. I did NOT connect them to the computer at all.
2. Only after I noticed a problem did I connect the drives to the computer, which showed immediately, corrupted file structure.
That's why I am sure that it was the OPPO.
chkdsk /f drive: works perfectly to fix the issue. I downloaded about 6 disc recovery "try before you buy" software - not one of them could identify and resolve this simple issue.
Let me know about the Dune. How ever, now that I know how to fix disc errors, I am going to try and use the OPPO for a while, for .iso files. I don't know whether or not I would need the dune. The oppo sound was noticeably superb. I have not yet tried the video a/b and toslink Vs 5.1 analog audio connection.
Of course, this time, I will use only discs which have been fully backed up! lol.