Nice to find another Chesky fan.
And another SACD fan.
I have no hard and fast rules about whether I listen to the 2.0 or the 5.1 layer. I switch depending on my mood. It depends on the recording and how good of a job the engineers did at mixing it. Some 5.1 mixes have an extra pop of realism to them. Others just sound like they're overdone.
If I had to make a sweeping generalization, I think that with older recordings newly 'upmixed' to 5.1 and released on SACD, I often prefer the original 2.0 mix. Then there are SACD's specifically designed for 5.1 'demos', and those are certainly much more fun in 5.1 than 2.0.
