The S20 is basically the pre section from the Trident 80 series. I've used the 80 quite a few times and have always been in love with the sound of the console.
A cool feature on the S20 is the ability to have 2 mics connected to each channel at once and be able to A/B them with a push of a button. A novel idea when your just not sure which vocal mic is the perfect one.
I always like the Trident 80 on drums in particular, although it is really difficult to get bad results from the 80 unless your a monkey.
Hope this helps,