This drive appears to not support any 8x DL media; if it does, it is likely to be sketchy. Also, the most reliable media is Verbatim's DL, and for your drive, you will probably be better off getting 2.4x rated media.
Also, as a tip, be sure to check some/all of your DL burns to ensure they can be read back well. I wouldn't trust burns on Best Buy/Dynex-brand media, and Sony's choice of media currently appears only to be the lesser quality Ritek DL models that are unreliable.
You will most likely have to return the TDK discs, or donate them to someone with a drive that can even remotely write them well.