You should have no problem. The heaviest item per square inch in your home is your refrigerator when full. It's even heavier than a waterbed per sq inch. There are lots of homes with frig's on the second floor. I have my record collection and stereo on the second floor of my house. My house is over a hundred years old. I did add support under the records but not the rest of the room. 400 lbs is about 2-3 people at most BTW.
How much weight can an upstair room can hold?
I was " confined" to 2 small empty bedrooms for my A/V gear(14x16 and 14X15)and they are both upstairs. I have added up the weight of all my equipments and racks/stands in one room and it's about 400 lbs so far . I am looking into some mono-amps and some speakers for the other room. Being living in a city that tends to have some " foundation" issue, is it safe to load up another 200 lbs equipments in the other empty room. The builder is no longer in business so ther is not much help there. Any one who is in the same boat can share a thought or two ?