Don’t get the JVC DL-R disks. They aren’t as good a quality as the Verbatim +R DL disks, and the TY’s are not well supported in the firmware of most drives.
You cannot bitset -R disks by the way. Only +R disks can have the booktype changed to DVDRom.
Buy Verbatim DL disks, either the 2.4x-6x or 8x disks will work in your Optiarc.
And I very much prefer using a free burning program called ImgBurn for DL burns. It will set the layer break correctly, though that particular problem doesn’t seem to be affecting you here.