Optical to Analogue Stereo (optical to stereo RCA connection)

I have my Airport express finally configured and my intention was to send iTunes to it. I used a headphone type jack which splits into a left and a right channel and this is connected to my stereo amplifier (no, there is no digital input - its solely for stereo) - Result - the sound is very 'tinny' to say the least (virtually no midrange and I have to turn the amp to maximum to get output sound). I started doing a bit more googling on the subject and it appears that the sound is impressive if I used an optical cable from the Airport Express to an amplifier with an optical in -BUT is there any way of getting good sound from my current setup - I looked at Optical/digital to analogue converters and they are quite pricey (I might as well buy a new amp with an optical in). Also most converters are optical to coaxial etc.

So, I'm pretty stuck on this - I'm sure there are others in he same position as I am - that is, want to stream iTunes to an old amplifier without any digital inputs?

Hope you guys and gals can help me out.