My entire system is on a 3rd floor and it weights way more than 400 lbs.The rack alone is probably 300lbs(sand fillable coloums)then I got the Rogue Zeus at 200lbs plus 2-3 other heavy amps,cd players,records,cd's,other gear,furniture,name it and it's up-there.I wouldn't worry about it.When they frame floors ,they take into consideration the live load and dead load.Beams and stringers deflect ,they don't just suddenly break.If you see hairline cracks on the ceiling below after you move your gear upstairs then you know you got too much load,but I believe you should be just fine.
Enjoy your system and the tunes!
George
Enjoy your system and the tunes!
George