I tried this "RioGrande" settings : I don't think that it's Billy's Marshall; maybe that one is one of Dusty's Marshall on Billy's side !
It would be cool to see the settings of the Marshall at the right of this one on the pix.
anyway, here are some short mp3s of my Pearly direct through my 67 Marshall 100W (nothing in between...) into a 4X12" basketweave
same settings as on the pix #2 : http://dicitte.com/images/RioGrande_settings.mp3 it does sound too "bassy" (personnal...)
my personnal "ZZ zone" settings : http://dicitte.com/images/ZZzone_settings.mp3
closer to Billy's Marshall tone and more woody (love that setting)
Gaston :salude
Sweet tone!
I have to add that Billy used the Super Bass and Dusty used the Super lead. Also the Super bass had a 500pf bright cap and Billy always ran a treble booster. His settings in the studio to live would be different. But still this is a great comparison.