Magnepan 20R vs 20.1Rs

Anyone know the difference between the Magnepan 20Rs and the current 20.1R version. I am pretty sure they both have the push pull quasi ribbon midrange (verses the 3.6s'midrange type panel) but I am not sure how the base panels compare. The 20.1 is a push pull diplanar bass driver. What is the bass in the earlier 20R? Anyone heard a side by side comparison. I tried to find earlier threads but with no results.