There are a lot of threads, but most of them are for power amps. I generally leave power amps on all the time. Source and pre-amp in standby if available and if not I generally turn it off. All of my high end source components have a standby--so the only things that do get completely turned off are not high end or are part of the HT. There are two issues to this: one is sound quality the other is realiablity. For amps it generally affects both (+ to leave on). For source components the heat generation is rather small (with the exception of some tube equipment) and so reliability is not affected as much by cyclical heating--however the sound might be. You should try your components on for 24/7. Then turn them off overnight and let them cool, and see if the next day when turned on cold if they sound worse. If so, how long until they stabalize--different gear takes different times, but most source equipment stablizes faster than power amps--but that is a general statement and not always true. You'll have to do some experimenting to determine it for your system.
