What is the difference between DTS and Dolby Digital?

Does my DVD player need to be compatible for DTS. I do not know if mine is.

Is the sound quality that much better between DTS and DD?

I have 2 QS8s, 2 M60s, 1 VP150 and 1 EP(Kicks A*s)500.

Do I need a single speaker for the back for DTS?

Thanks