does any one know of a cheap way of getting 5.1 surround sound from the playstation 3 using its optical output

Answer 1

Depends on how you define cheap.
You can buy a 5.1 speaker system from Logitech for less than $200 (see www.logitech.com) . You can probably find it cheaper on ebay or from other retailers.
I am sure there are other PC-oriented 5.1 speaker systems.

Or buy a low-cost home-theater in a box, but make sure it has an optical input as well.