Here is what the Mk II manual says, and I own both the I and II and they both operate the same in this regard, and no harm comes from leaving the unit powered on:
The front panel PS logo button, located on the upper left hand corner of the unit, is the Ready/ Operation Mode control for DirectStream MK2. This control has two modes: Ready Mode and Operational Mode. Ready Mode (Idle) is designed to keep power on to critical internal circuitry, including power supply capacitors, thermally sensitive semiconductors and integrated circuits. Press this front panel button to activate the Ready Mode or to place DirectStream MK2 in Operational Mode. When pressed to activate the Ready Mode, the display as well as the outputs are turned off, but all the unit’s critical internal circuitry remains active. If you wish to conserve energy consumed by DirectStream MK2 it will be necessary to use the rear panel power switch. Using this rear panel switch will remove power from critical components. In order to gain maximum performance levels, you will need to turn DirectStream’s power on at least 1 hour before use.
As far as the power amplifier goes. . . I don’t own one, and own tubed amplifiers and generally turn them off when not in use and monitored. When I did own a solid state amp, way back in the distant past, I often left them powered on indefinitely and don’t believe there was any downside to doing that. . . but I have not owned a power amp exactly like the PS Audio and don’t wish to misguide you.
After I did some research and wrote the Copper articles (the summary being in Issue 205) about power consumption, I now turn off everything when I’m done listening. The DAC draws nearly 22 watts in standby (DS Jr.), the streamer draws over 4 watts (AirLens). If I spend most of a week listening to vinyl and don’t touch the digital side, there’s no sense in even turning those on. What’s even more frustrating is that the power conditioner I use for the lower-wattage components itself draws over 4 watts (with nothing plugged in!) and the only way to stop that is to unplug it from the wall.
With all the cuts I made in the house to power usage, I’ve trimmed our monthly bill by $20-$25. Those with deep pockets obviously don’t pay attention to cost, but I’m not made of money and the more I can trim our cost of living, the more things we can enjoy in life.
My current process is to turn everything on and start playing music. I figure it takes about an hour for everything to come up to stewing temperature, so those first couple of plays I don’t really pay much attention to, and/or wrap up other activities before I settle in for an hour or two of listening. I try not to overthink the warm-up process–if everything is warm and “heat-soaked” to the same temperature, it should be good to go.
Remember that the BHK 250 has two tubes in it. Putting it in standby, either with the “off“ button on the remote or using the blue switch on the front, turns the tubes off to extend their life, but leaves the main portions of the amp powered up. That’s what I do unless I know that I won’t be listening for a few days, in which case I turn off the switch at the back.