You always get surround if you run HDMI to a receiver.I have my GTX 560i connected to my 32"TV ( as monitor ) via HDMI but I use the coax to stick it to the z5500.
Not to hijack this thread but can u actually get 5.1 DD on say BFBC2? Or is it even available. I know my connections are fine as I get that when wathcing DVDs or Bluray.
With optical or digital coax, you only get surround from a game if your soundcard/mobo supports Dolby Digital Live or (even better) DTS Connect, which allows encoding of audio on the fly into one of those surround formats. (Movies are pre-encoded, so they always come in surround.)