The Ref 30 is a total upgrade from the 20. The most notable new features (for me) are..
1. New Motorola DSP - this puppy is much faster (on paper anyhow)
2. Selectable notch filter(s).
3. Room acoustics setup. Built in tone generator.
4. 3 zones output - all with video and digital sound.
5. firewire input (so you can connect your digital camera... j/k)
6. more bass management than you could ever need. - no flames please.
Thats all that comes to mind. Correct me if I'm wrong, but weren't the DACS upgraded in the 30?