Cheapest way to convert from toslink to 4 channel analog audio? I have a mac-mini and an old analog 4.1 set of speakers and I want to use all 4 channels instead of only two.

I do not have a receiver and I am looking for the least expensive way of achieving 4 channels audio working.

I should also mention that the mac mini does have an HDMI out, so this could contain some audio out but I'm not sure how many channel it does have and I do know that my TV is not able to convert the signal to analog (and it's speakers are far worse than the 4.1 old system).
I use a Behringer ADA8000 for this - it converts toslink to 8 channels of analogue, and vice versa.  It works well, and is relatively inexpensive.