I thought about trying DVD-R DL discs but I was unable to find any locally. I ended up buying a new drive to-day. My original drive is a LG CH10LS20 and was fairly expensive as it reads Blueray as well. I bought a Samsung SH-224BB/BEBE to-day for $20 and installed it.
Cheaper than buying another 50 pack of DVD+R DL discs.
Anyway I tried it just now and MyDVD was successful in burning a Dual Layer disc at 8X write speed and Fit to Disk. So it appears that my problem is solved.
It is a mystery as to why Cyberlink Power2Go would work with my LG drive and Roxio failed every time.
Thanks for everyone's answers to my request for advice.