ned said:
The SL2 was a standard hot rod Marshall module offered by Egnater. The SL++ (I think this is correct) is more a Slash tone module built by Jeff at Egnater, there are fewer of these but back in the day they were pretty easy to get - you just had to order once directly from Egnater.
^ Pretty much this - Egnater offered a SL, SL2 and SL2x SL = superlead (plexi), SL2 = hotrodded superlead, SL2x = even more hotrodded, the GNR mod if you like
Youtube of a Egnater SL2x:
https://www.youtube.com/watch?v=sdc22Y7-d2k
Bruce also did a dual module of his EG preamp called an EG3/4 which was very like the SL2 but a bit darker, and a hot rodded version of that called the EG5
Hope that helps!
EDIT: list of modules by Bruce (from here:
https://www.rig-talk.com/forum/threads/egnater-modules-still-available.123035/):
Bman Bassman (Like a 4x10 Bassman. Beautiful, warm clean to approx. JCM800 gain)
VX (Vox AC30)
SL (moderate to fairly hot Marshall=clean to AC/DC)
SL2 (takes over where the SL leaves off. Fairly hot to way high gain Marshall)
SL2X (Tighter and brighter version of the SL2)
T/D (Twin/Deluxe. Really clean Twin on 'A' to pushed Deluxe on 'B')
COD (California-Over-Drive. Our take on the singing, strong midrange Mk11C/Dumble-ish thing)
Erect (Dual Rectifier)
EG3/4 (Channels 3 and 4 from the TOL amps and IE4 preamp from long ago. Smooth, singing with tons of gain)
EG5 (A tighter and brighter version of the EG3/4)
MHG (Modern High Gain) Mid scooped, quite high gain, very aggressive.