This is the only tolerable JCM900. The SLX is a single channel that was meant to be a hot-rodded 2203 JCM800. They added a bunch of diodes to the circuit and goosed some extra gain from the pre to make massive shred sounds. If I recall it has an effects loop. Which is lame and un-marshally. But everyone in the 80s had to mod their 2203's so they could use their huge racks of digital processors, so by the 90s Marshall decided to get with the program and give the people what they wanted.... then "10" and "Nevermind" hit the shelves and the poor old 900 went right outta style as 70s EHX and MXR stompboxes flew off the shelves of pawn shops everywhere. Those were the days!
In this vein I think the Silver Jubilee sounds a lot better... and even the channel switching 800s have the edge on the 900SLX to my ear (though not by much). Still, the SLX is pretty tolerable (when compared to the rest of the 900 series that is) and you can use it to amplify your guitar in a punk or hard rock setting if you don't have a real Marshall at your disposal. I just gave you the skinny, so caveat emptor on this overgrown paperweight.