Dunno Y U R finding bass lacking, but it is unlikely to be anthing to do with impedence matching. It's usually best for in transferring audio for the source impedence to be many times lower than the destination impedence, and this is just what you'll have.

Cans outputs are designed to drive impedences down to 16 ohms or so, and will find the 10K+ impedence of a hi-fi a very easy ride, so something else is responsible for your poor bass. Do you have access to a frequency sweep? Record it in 'sound recorder' and replay it in Windows Media Player using the straight scope visualisation. Even better, a white noise source could be used and displayed using WMP 'bars' visualisation. If you have a more sophisticated sound program the input meters should tell you what you need to know.

Whenever you have digital audio to transfer, do it in the digital domain; converting to analog and back again is a real bad idea.