I've never heard of 2-channel-only toslink. Toslink is Toslink. It's digital and it's up to the software to throw in however many channels of data. What your computer spec suggests is most likely that the sound card hardware encodes only up to 2 channels into Dolby 2.0. However, on all sound cards that support digital output there's a bypass mode that sends whatever Dolby 5.1 signals from the source (e.g. DVD) to the digital output unmodified.
Furthermore, ffdshow audio decoder is a very powerful tool that can convert any source into Dolby 5.1 compatible streams live (e.g. it can take 2-channel mp3 music or even 2-channel live analog input on your sound card and uses the decoder's cross-channel matrix/reverb/DSP and feeds out a Dolby 5.1 stream onto Toslink/Coax).
However, most HTIB with DVD player includes NO digital input. The only 5.1 source of these HTIB's are from the internal DVD player, or perhaps at most 1 digital input. The spec of the Samsung HTIB your link points to doesn't seem to suggest any digital input. I highly recommend going for a 5.1 sound system WITHOUT a DVD player.
EDIT: The Samsung in question does input 1 digital input. These days everything has digital audio output and you can easily run out of digital audio inputs for your sound system. I have a Sony 5.1 sound system (without DVD player) and it has 1 Toslink and 1 Coax digital audio input and it's way too few. I end up getting a Joytech 7-component-input (5-Toslink) switch to cope with my rig (I don't use the component video switch). I have 1 HDTV, 1 Shaw HDDVR, 1 DVD recorder, 2 computers. That's 5 digital audio inputs already. And I haven't counted game consoles yet.