If there is any converter from optical digital sound to analog full sorround?

There certainly is. Its called a Multimedia receiver. You an get one for as little as 250 dollars. Will output surround channels from Optical digital, Hdmi, virtually any surround source, even has built in radio reception, hooks up to any DVD/ Blueray player, tape recorder, Ipod, whatever, you may have or get.

The converter ChrisL linked to is for PCM (stereo) optical to stereo RCA. This is not the same as DD5.1 optical from a HDTV, BluRay or a DVD player.

The device you want for optical 5.1 to 6 RCA analog outputs is this:

http://www.amazon.com/Premium-Audio-Digital-Decode...

There are converters http://www.amazon.com/s/ref=nb_sb_ss_i_0_10?url=se... but you will not get 5.1 or 7.1 surround sound. RCA will get you stereo at best