Hey soix,
1) Fully balanced
2) I do leave it on 24/7 and it gets relatively hot, but not hideously so.
3) When taken out of stand-by, I would say about twenty minutes to start to sing.
4) The S5.5 gets the tonality/colors of the AricAudio tube gear, and then adds transparency, bass control, and dynamics of great solid state. The S5.5 also has one of the best top ends of any amplifier, solid state or tube based, I have ever heard.
Teajay