A single tube?
Well, it could be a double-something (maybe a double tetrode or pentode) to do two channels, but certainly not enough to do an entire 5.1 sound system.
I suspect many of the perceptual advantages of "Tube Sound" could be achieved more easily using JFETS (semi-obsolete in favour of MOSFET), as they have a rther similar curved characteristic - which also made them great RF mixers until dual gate mosfets and packaged double balanced mixers took over.
I'm not sure you can "cheat" your way to true valve sound, not without using them in a power amplifier, driven HARD.
Valves (I'll slip into the UK parlance here) produce significantly more distortion than competent solid state technology, but their tendecy to "square law" curves, softer cutoff and saturation, means it tends towards "musical" second harmonic instead of the harsh odd harminics of overdriven solid state technology.