Forget amps, that setup is more than adequate. (No offense, S6!)
Get yourself some Ken Smith Slick Rounds and those triangle Telefunken picks that Brad convinced them to reissue. Find the right pick attack and you'll be nailing it. I'm getting that tone on my Sadowsky 5-string J-bass, even through my practice amp. It's really kind of the "Wrong" bass and amp but it works great.
You have to buy a 4-string set and add the B and C separately:http://www.juststrings.com/kensmithelec ... round.html http://www.juststrings.com/slickroundke ... rings.html
I got a dead low B from these guys... I should probably tell them, I bet they'd send me a free replacement.
These are the picks, available only on Ebay but they're legit. (there's a whole thread about them here somewhere) http://www.ebay.com/itm/TELEFUNKEN-Grap ... 314wt_1139
You can come close with the 2.0mm Adamas graphite picks that all the Jerry guys use, but these triangle picks get the tone you're after so much easier. Edwin gave me one and I thought it was too weird at first, but I gave it a chance and now I love it.
Scoop the mids a little (turning up the Aural Enhancer knob on that GT/SWR preamp will do fine) and you're there.