If your 777es is anything like my 9000es (I would venture to guess "yes"), then I may have a solution for you. I also thought that my 9000es would not play CD-Rs based on the research that I've done on the threads here and elsewhere.
It turns out (kudos to George Louis of RCCD fame for this) that I have been successful in 9 out of 10 burns, using Maxell's MusicPro CD-Rs. These are mfg'ed by Taiyo Yuden in Japan, and are a bluish green color. George said these were decent for sonic quality.
I bought mine at Walmart.
If you try it out, let us know...