Can temperature fluctuations affect audio gear?

If you plan on using the system,I would open the door,and blow a fan on it(system),while it warms up.Maybe a hour,or so first.The warm humid air from downstairs,plus your humidity might cause condensation in them,if it gets fairly cool.

The amount of heat your gear will 'give up' to the environment is related to the difference in temp. If your amp runs at 100f in a 100f room, very little heat will be transferred. In a 65f room, you've got no problems.

During the hot part of the year, at least make sure you are well ventilated or perhaps even install a fan near any hot gear.....But be careful not to just blow at hot stuff, if you restrict the natural convection, you could possibly even make something run warmer...while trying to cool it. Any fan I place is above the hot piece and blowing AWAY to suck air thru the piece and allow 'nature' to do its work.

And from our FWIW department, those nutty radio astronomers run their amplifiers and much electronics in a liquid nitrogen bath at colder than -320f.
This is to reduce the 'thermal' noise of atoms bumping into one another. In the very highest resolution systems this may make a difference. Or not. LOL.

Other temp effects may be on the speakers where characteristics of some synthetics....perhaps woof cones, may change from the coldest to warmest temps encountered. I'd also suspect greater power handling capacity in the coldest weather. The voice coils will cool much better.

12-03-10: Magfan
The amount of heat your gear will 'give up' to the environment is related to the difference in temp. If your amp runs at 100f in a 100f room, very little heat will be transferred. In a 65f room, you've got no problems.
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Maybe you were trying to say something else, but it didn't come out right. The electronics will essentially be at a constant delta above room ambient (more or less). If your amp runs at 100F when the room is 100F, it means that at 65F room, the amp would run at 65F. Of course, that isn't going to happen.

If the amp is at 100F when the room is at 65F, then when the room is at 100F, the amp will be at 135F. The heat transfer is constant, that's why the amp runs at a constant delta T above ambient.

The ambient temp can effect speaker performance. I experienced this first hand with a pair of Monitor Audio Studio 20s. Below about 70° the sound would lose its openess. It could be due to the metal cones in the Monitor Audio, but I haven't noticed the effect with other metal cone speakers I've had.

I could easily see how the cold could effect a listeners perceptive abilities both positively or negatively.

I see how I miswrote. But I'll stand by.....that as the temperatures of the room and amp get closer together, heat transfer slows.
Point is, cooler is better and you can cook it in a hot environment.
Heat and temperature are 2 different things.
And NO, the amp won't always be the same temp delta from ambient. In SS, for example, you have a max temp possible....say the junction temp of the devices. In a hot room wont' the difference drop as the room temp approaches junction temp? Or will the junction keep getting hotter until failure? Isn't there an upper limit to the temp of an amp?
2 amps of identical efficiency and power rating being run identically will be at different temps depending on the mass of the amp. And we all know how much heatsinks cost.

It's kind of an aside, but look at a few Stereophile amp tests where they 'precondition' an amp at 1/3 power for an hour before bench measurements. Some amps fail.

I'll call a friend of mine who is a PHd in physics. he'll straighten me out. His area of expertise is semiconductors, so it'll be good info.