Will leaving an amp powered-up all the time...

Some class A/AB amps are designed so the bias adjusts more toward class A (class A = semiconductors on all the time) during warm up, theorectically so they won't sound like junk prior to thermal stabilization. Never heard of cap saturation in a negative context. It sounds like a good thing. Caps are the storage batteries for the amp. The worst case scenario with caps is insufficient capacity where they drain too fast when you need them. Keeping them filled is the big, heavy transformer's job. Like an automobile engine, the amp's system should work best over the long haul operating at its designed thermal equilibrium. I leave mine on all the time.

I noticed the same thing on my Pass X250,5.After 3 days being on,it sounded too bright and underpowered.The regular1 hour warmup sounds a lot better.

Amps ofen need to warm up to sound their best, I also leave mine on all the time