The LiteOn 851S generally prefers and writes a bit better to +R media. Not to mention the fact it can burn certain +R media at 8x while -R is limited to 4x.
To make +R media more compatible with set top DVD players you can use the bit setting tool provided by LiteOn (check the LiteOn tools guide in my signature for more details).
You have to make sure to feed the 851S with good media otherwise you are asking for trouble.
Head over to the LiteOn forum and have a read / search for answers. The 811S/851S are very popular right now and you should be able to find most of your answers there.