Echoing the thoughts here that the SL68 is one of the last amps left on my must-haves list. I'd love to pick one up at some point. Out of all the plexis I know about, the SL67's and SL68's are particularly cool because they can be dialed in to sound like the amp is going to actually explode, like it is genuinely being driven way harder than it was ever meant to. I have no idea how they do it but if you crank it up enough, something happens where the highs and mids start to move from overdrive and clipping to straight up fuzz and it's so awesome.
Here's a video I found of a really good example of what I'm talking about:
The Master Volumes on those amps are neat as well. They're better if you think of them more as a reverse Tone knob. Basically, start with the MV on 10 so it's out of the circuit, then dial in how much distortion you want. From there, if the amp gets a bit dark like Plexis can get when you turn them up, slowly turn the MV down until the treble gets un-squashed by the poweramp clipping and gets a bit more breathing room. You keep all the crunch and gain you get from driving the phase inverter but you get back some high end detail. Super cool.