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 ?
Back in my more "recreative" days, I was renting the upstairs apartment of an old farmhouse and fell asleep in the living room while I was filling my waterbed. When I awoke (about 3 AM) the height of the top center of the bladder was above my waist line (and I'm 6-3). Given the weight was probably over a ton, I was very lucky it didn't crash down onto my landlords dining room table and kill someone. I told him about it a few years after I had moved out. He thought it was hysterical. He died some years later in jail from alcohol withdrawl serving DUI time. I have absolutely no idea where this was going but at least BE ALERT. Yeah, I know, the world needs more lerts. FWIW
YOu can ask your local building official what your state building code is based on for a residential structure second floor. Also you can figure that a 200 lb amp = one fat-a$$ed American and draw your own conclusions. And remember that most building codes would be based on a load in terms of weight per square foot so a 200 lb amp is probably providing a similar load to a 200 lb person standing up.
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.
you could easily get a ton of people (just 10 to 15 persons) in that room and not think twice about it.

I would not worry...
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!
Older house has an edge because old trees are denser and can support more weight.

You can always spread out the pressure point by placing a platform under your rack, can act as vibration damping device as well.
I would check the distance between joists if I were you.
They used 24" centers alot and the joist is usually a true 2X6 in older houses. Today it's 16" centers and the joists are 1.5"X7.5" at best. The issue is, will 24" centers with 2’X6”s hold enough weight? Maybe, but when I remodeled my 3rd floor they made me add joists between the existing joists and onto the existing bowing 2"X6" joists to bring it up to code.
No problem.. But if you line the walls floor to ceiling with LPs.. At about 4,000 equals a ton..
I knew a guy who was evicted because his 30,000 LP collection was causing the ceiling in the apt below to crack open from the joists sagging.
Thank you, guys and thanks to a friend who warned me. Yes, I just now notice a crack about 6 " on the ceiling of the garage where I have put my main rack on the carpet floor in the room above . I wonder what kind of house Kimball Hills built but the house is less than 10 years old and it ain't a cheap one either. It 's time to get busy to pack all the gear and gets rid of them at a loss a again. Time to get ICE stuff. It's just a story of my bad luck.
1 crack is not a problem. Cracks happen throu out the life of a house. They happen as the house settles. Watch the crack and see if it gets longer and you could also have someone come and look at it. No reason to get rid of anything.
Hevac1 is correct. one thing you can do is use some tape to mark the ends of the crack to see if it is elongating. Elizabeth is correct about storage of LPs, but 500 lbs of gear should not be a problem at all. Also consider where the gear is located. If its arrayed against a load bearing wall and spread out so its over several joists, then the load on any one joist is small and transferred to the vertical load-bearing studs and plates that are designed to carry much bigger loads. If you are really worried about this, call an architect or structural engineer. Would be well worth a couple of hours of their time (if they charge you at all; they may be able to answer this question very quickly in a brief phone call) considering the cost and hassle of selling all your gear.

I am a carpenter, general contractor and builder of all things great and small for my entire life.

A 10 year old house following the standard building codes would allow for 40 pounds per square foot of live load for your floor. Taking 1 room of 14 x 16 with a total of 224 square feet x 40 = 8,960 pounds equally distrubited throughout the room. A 300 pound refrigerator of 33" x 36 " = 36 pounds per square foot. These days lots of folks weigh in excess of 300 lbs. and occupy 1 square foot. I have never heard of someone falling through a floor or colapsing a floor. These loads a very conservative

You have absolutely no worries for your stereo or anything else in your home.

The crack is probably a drywall seam.

Enjoy your system and stop worrying.
Leatherneck 1812, thank you for the assurance . Now I have something to show to ther other half that the crack on the garage ceiling does not come from my heavy gear located in the bedroom above. It's bad enough to be confined " out of sight" these black "boxes" in a small square feet room....
Andrew- If the crack is in your garage ceiling and the garaage is unheated, its probably a thermal expansion/contraction thing, esp w a heated/cooled room above.