I took hope from alexnoes statement and tried the 755A with the multiple rewrite strategy. Well, after the third try, the disk could not be rewritten! All Plex drives then refused to format the disk any more. This disk can still be rewritten nicely in a LG-4167B, but even after verifying the legibility of the produced disk, it won't erase anymore in a plextor drive. This technology never ceases to amaze me...
I then turned to work on a 716A, and used that same multiple rewrite strategy with a used Ricoh +RW 8x. The results are not bad. The drive finally creates disks at 8x that stay below PIE 280 and will hopefully play downstairs. Just for the sake of curiosity, I wrote the same data again in the third run, and the result is obviously not representative. So one should change the data when doing this.
As a consequence, I am going to remove the 755A and wait for better firmware or Verbatim DVD+RW 8x. I have found some reports about that media, but didn't see a place where it can be bought. Anyone? What do all these people use, who bought these 8x RW recorders?
I attach the scans I made. First is the scan from the mentioned LG drive, written at 8x. Looks so sweet - perhaps thats why the Plex drives won't erase it any more?
That scan is followed by the mighty KING OF QUALITY 716A, burns 1,2,3,5 on the 716A after an initial "full erase".
Please feel free to delete the scans if I violate some rule about it.