I have a 5 or so year old receiver (sony STR-D515) that I know doesnt have all the decoders of the new stuff. The thing is its in great shape with little use and I have all the matching components
VCR, CD and DVD players

I did upgrage to a nice 5.1 set of Polk speakers that sound incredible on the reviever.
I want a decent surround system and dont know if Im missing something by not getting into a new unit.

The spec sheet for the STR-515 says it has
"3 types of surround effects"
"Dolby*Pro logic and Dolby Surround Pro Logic"

Are those really three kinds?

My main question is:

Am I missing something I need to have or can I live with this one?
I only have the 5 speakers and a sub

The room is 15x15 feet

Any help is appreciated
DMC