Error -9356 seems to "be command on IDE bus timed out" after some googling.
Initially, after installing the drive, I created several coasters until discovering that the G4 (or G4 extensions) were connected to the problems. Here are notes from the tests with G4 extensions enabled, and the cache set to write-through mode (slower but more stable):
Speed Prepare and Write Finish Actual Speed
16x 406 s 22 s 7.01 x (!)
16x* Buffer Underrun
16x** Interface Error -9356, Freeze
*write-through cache, BurnProof Off
**write-through cache, Power Conservation, Thermal Monitoring, BurnProof On
When the write-through cache was disabled, burns always ended with underrun (BP Off) or -9356 error and freeze (BP Off) and a coaster.
Is it possible to use different writing speeds in Toast ?