Gain wise, they are close, although SL2 Ch A probably has a little more on tap.
Tone and feel wise they are different. Ch B of SL has a different vibe to it. It is not as smooth as SL2 CH A and has more of a vintage voicing in the mids. Low end a little looser too. SL module just has looser feeling with the gain up than the tighter, more modern SL2.
Truth be told, I prefer the SL to the SL2. Much more versatile and I've found it very sensitive to preamp tube changes. With a good OD pedal, the SL module is my favorite. I've had good luck with BB preamp, Sparkle Drive, TubeScreamer and BK Butler Tube Driver.
I havent played the SL2, but I do own the SL and EG3/4. I would agree that the SL definitely has a looser more vintage voicing. Feels great to play and takes pedals really well. Channel A can also be set fairly clean, especially if you are a Strat player.
Neither one is very compressed, but the SL definitely has the more open, vintage sound. Not as compressed. They both have no problem cutting through in a mix.