The Plextor drive doesn't care what device the media was burned on. It has no "decision" making capabilities for 'bias'. The drive is in a read operation and burning does not enter into the equation for Q check graphing. The PTP application just reports the PI/PO or C1/C2 results as read from the drive, so it cannot be biased toward one media or another. It just processes data.
The PTP Q check is designed to work with Plextor drives only, but the app will test any drive for write transfer or read transfer rates. The write transfer and read transfer are tests of the interface, laser and mechanics, and, unless the media drops off due to burnproof or PoweRec, is not a check for media quality
A better test would be to take multiple blank media and run them in the 760A to test for FE/TE at max speed. Take four or more discs with similar/identical graphs. It is possible to get varying results within a spindle, so you want to start with identical media, or as close to identical as you can get.
Burn two in the 760. Run both completed discs burned on the Plextor through a full Qcheck for beta/jitter and PI/PO sum 8 to check results. They should compare fairly closely.
Then use the Sony with Nero or other testing program to burn and test the other two discs at the same speed as the Plextor burn. They should compare closely in the test program.
You can test the Sony disc in the Plextor to see how it reads, and check the Plextor disc in the Sony to see how it reads. The results may be different, even if you started with identical discs.
You cannot compare QCheck results in the Plextor against Nero results in the Sony unless you start with a professional (CATS, Expert Magnetics, Clover, etc.) tester system that will give an 'unbiased' baseline. You are then comparing the PTP or Nero results against a dedicated test system, instead of one app vs another app. Each application may process the errors differently and you'll get different results for each disc tested in each drive, simply because of media differences and hardware differences.
You may get consistent low errors in one drive with a specific media recorded at a specific speed, while the same media gives varying or high error results in another drive at the same recorded speed because of the write strategies. Try selecting the various modes of Autostrategy in the 760 if your results are not consistent from disc to disc.