Thanks goodseed. That is not what I was talking about although that program does make it handy to be able to compare reference material to your own mixing and mastering projcets. I don't need it though as I have lots of inputs on my digital mixer and can bring incoming sources in easily and also control and match their levels and switch to those sources fast.
 
The Foobar concept is what I am after. I wanted to be able to compare very similar sounding things and not know which one I was necessarily listening to and try to work out which it was. As Mike says it can be quite humbling, I agree.
 
Especially when doing things like comparing the sound of two different DAW's. Sometimes it is easy to assume that one sounds SO different to the other but once you get into the Foobar thing it changes big time and you find yourself listening to (very) identical things trying to ponder which is which. People who swear they can hear massive differences in things would fail miserably under certain test conditions. I have seen it many times.