To be honest, I'm incredibly uninterested in the supposed 'valve sound', I prefer a bass to sound like a bass - this looks like a simple little preamp that would be easy to build. Using FET's of course gives it a nice high input impedance suitable for matching a passive guitar.
I wouldn't worry about multiple stages, every valve amplifier you see uses multiple stages - as I see it most of the 'valve sound' comes from heavy clipping of the push-pull output stage, which is comon for heavy metal and rock music.