^ screw Voodoo mods... I have a huge problem with them covering the circuit in black apoxy meaning if you ever need a recap or a component in there goes, it's cheaper to replace the amp! Plus I've heard before and after clips of their JCM 2000 mods, and couldn't really tell a difference, they were both super fizzy, could pass for solid state, etc. And the clips on the site sound like a stock JCM 2000 as well.
JCM 900s aren't nearly as bad as some people say. The trick is you have to get them properly biased, and probably some better tubes too than they shipped with. They came biased so cold from the factory that they sound like cr@p brand new and everyone's like "omg these things are thin" but that couldn't be further from the truth. If it's a SL-X, than it's an even better deal ;)
Rubys are rebranded Sovteks or JJs.... nothing too great, but not the worst either.
And damn steve you get a mean tone from a JCM 900!
And yes it has enough gain for almost any high gain Marshall sound.
Steve Vai used JCM 900s in the early 90s as well.