Just to be sure that we're talking about the same stuff.
With feature code you mean feature codes returned by the MMC GetConfiguration command (0x46)?
-R DL sequential is handled by feature 0x002f, layer jump is handled by 0x0033
If you only discovered these values on Plextor drives, maybe it's something that is limited to Plextor drives. Gigarec, Varirec and all this stuff.