Listening after your entire system was powered off cold for a week+

I don't have to disconnect anything for any amount of time to notice a difference upon start up. Whether it's the analog end, CD player or streamer, they always sound better after a half hour to an hour warm up. And keep getting better after that. Unfortunately that's the reality in my system. And no, it's not my ears getting used to it. Such is life when your system gets to a certain level. On a radio shack system it would sound the same cold or hot. Or at least you would not notice the difference. 

I leave my solid-state preamp on all the time.  The solid-state AB-class amps need 15 min. to sound right, and perhaps improve with more time on.   I would expect the system would need some time to warm up if the preamp were turned off, even if just a day or two.

My system sounds good after 12 hours, better at 100. Pre-amp only goes cold for extreme weather.

The OP’s system needs more time to warm up after a complete shutdown. Perhaps some of his equipment has a ’stand-by’ function, which ’sort of’ keeps it warm.

Most class A or class A/B amps and preamps need time for their capacitors to charge up and stabilize. The same for most tube devices as well.

Yet one more report of 1/2 to hour for better sound on a class A tube integrated. (If house AC isn't on all the better too due to white noise.)@decooney A whole house surge protector is your audio, AC and a raft of other electrical things in your house's new best friend. I also yank plugs... why not be better safe than sorry. A brown out once fried all our ACs and a few other goodies.