Hey Jim, Many thanks! I am still stunned that anyone watched this video, and then actually posted it here.
I typically do use D'Addario's on most of my guitars

. In this case however, they were Curt Mangan rock and roll strings, PORTCM12NW 1042. I got them at The Pick of the Ricks. To be honest I really don't think the strings make as much difference as a few other things do. But they are NOT flats as you speculated.
Yes I was using my original Jangle Box set to bright, with the knobs both set at about 12 oclock. The rest of the sound really comes from EQing and a little reverb.
I use Pro Tools to do my recording. Once I got the basic track recorded I then played with one of my EQ plug ins as I listened to the track until I got close to the sound I was looking for. I wish I could be more specific for you on this, but I find for me that is more a process of trial and error each track. I'd say however in my limited experience that proper EQing is at least as important as any compressor, or set of strings you use.
Here's another tune I did a few years ago where I was using D'Addario strings, my Jangle Box, set as I mentioned above, but with just a slightly different EQ setting.
http://www.youtube.com/watch?v=UaaMBD2ClEs
As far as the harmonies for our version of SDCAT, Joe on the bass, is doing most of the high vocals you hear. He is amazing on both guitar, as well as the harmonies, in any tune we do. Karl from this Ric forum with the LERM in this one is not too shabby either!! Thankfully David, who, does a better Roger McGuinn than Roger does, agreed to do the drums on this one, or there would have been no place for me!!

. Actually that worked out great, because his drum work here to me was outstanding.
It was a fun project to do, and most of it was done swapping files coast to coast. This was the first video I edited like this, using green screens etc, so figuring out how to drop us all into the scenes was lots of fun too. Hopefully I can get these guys to agree to do another one at some point. Meanwhile I do need to work on my lip syncing!!!
All the best, Al