Edit for Final Answer:
Looks like this might be just what you are looking for. It should be fairly simple to convert the output from it into any wiring type your speakers use. Only drawback is the cost, at $600. Hopefully it's in your budget.
You also might look on the back of your TV to see if it has any Audio Out connections. Most TVs sold currently will have at least one type of audio output on them (typically either Digital Coaxial or Optical). Then see if your speakers/receiver have a compatible input.
EDITed to include comment in answer
OK. After searching amazon.com for a couple minutes I found the following adapter. It shouldn't be too hard to convert that into whatever inputs your speaker system has (although it does look like you'd lose any native surround signal). If you need to keep the HDMI video signal for your monitor, then a simple 2 way split before the coverter would do the trick. Something like this.