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

Overhang, I personally don't consider the amplifier warmed up if it is just being left on. Doesn't matter on for 3 days or on for 3 weeks. It will not sound the same as if it had played music for 2 hours. With your amp it makes very little difference between on and standby. A signal needs to pass through. That's been my experience with the X250.5. I've left it on and not playing. But it sounds better when I just turned it on and ran some music for an hour or 2 before listening.

Arthur, Pass amps are known for needing bias adjustments every so often? Is it official?

As recommended in the owners manual, my Plinius 8200 mk II integrated is left on all the time (unless I won't be listening for greater than 5 days). Pliniius states the amp needs atleast 24 hours of warm-up to sound it's best.

I have a Pass X-350. How do you adjust the bias.

Thanks Audphile1.I will try it out.I never thought that a signal must pass thru in order for the amp to sound best.I thought the small voltage is passing thru from the preamp to the speakers anyway.