I have a 23.5 (very similar to your 27.5) for 16 years now. For years, I turned it on and off at the beginning and end of each listening session -- this because it was part of a bi-amped system with a pair of tube monoblocks. So when the tube amps were powered down, I just turned off the Levinson too.
For the last couple of years, I've been using the 23.5 only. I turn it on every morning, and off every night, and the rest of the system stays on. During monsoon season (just ended, with lotsa lightening!) when a thunderstorm is approaching, I turn off both power conditioners and the whole system is shut down.
In all that time (knock wood!) I've never had a problem due to power surges or lightening strikes. And the 23.5 ? Sounds as beautiful as the day I bought it. As a side note, according to the watt meter on my power conditioner, it takes about 5 minutes after turn on for the Levinson amp to settle down to a constant idle current.
