I must say I am pretty sceptical about the green stand-by, which reportedly "consumes only 2W".
2W per hour is that minor, so only reasonable explanation might be that the green diode itself consumes the whole 2W. That means that during "green stand-by" all major power supply circuits are essentialy fully disconnected yet, out of current, so that a real warming-up of amp actually does not occur. Real warming-up, of course, occurs during so-called "high current stand by" (red diode), which consumes some normal 150-450W per hour, depending on Evo-e model. However, this normal red-diode-indicated stand-by is being already known from the original Evo (not "e") series.
What does it means? Well... Ask Krell's marketing department...
BTW, I am happy Evo-400 (not "e") owner. Would be perhaps a bit more happy if own a pair of new Evo-400e, not because of the green stand-by but because of other improvements (reportedly slightly upgraded power supply, increased filter capacity etc).