Assuming you have a high quality, revealing system, I vehemently disagree with the above posts. All of your equipment except the tube amps should be left on 24/7 and powered down only if there is an electrical storm (in which event everything has to be unplugged, not just turned off). A high-quality system will not sound anywhere near optimal if the equipment is cold -- as a general rule, circuits take many hours to stabilize, especially digital (at least twenty-four hours as a general rule). And just so there is no misunderstanding, this advice also holds true for tube preamps and other equipment using small signal tubes -- the small signal tubes in tube preamps, tube CD players and tube tuners pass very little current, and the studies done in the 50's proved conclusively that they last much longer and sound better if left on 24/7 so they are not subjected to the deleterious thermal cycles that occur when they are turned on and off.
Tube amps should generally not be left on 24/7 because the output tubes pass a lot of current and they will wear out relatively quickly. There is also a safety issue, as most tube amps do not have tube shut-down protection circuits. I have VAC Renaissance 140/140 monoblocks, and the output tubes require three to four minutes to come up to temperature. I do not drive the amp with music until they have been on a good hour, however, as it takes at least that long for the rest of the amp to come up to temperature (the VAC's are a hot-running, class A design).
If you have budget equipment or object to leaving equipment turned on for environmental reasons, then turn everything off. But if you have good equipment that you don't want to break and that you want to sound its best, leave everything but the tube amps turned on and give the amps fifteen minutes to a half an hour before playing music.
