Does anyone experience sound improvement from restarting power off and on of DAC?

No idea what a one minute shutdown would cure, and especially with the DAC getting hot.

@mitchb - I would contact PS Audio and ask them.  PS Audio DACs are different from pure chip based DAC as they use FPGA (field-programmable gate array) with custom software to process the signal.  There could be a problem there.  Also, have you upgraded to the newest software version?

...From PS Audio's sales brochere:

DirectStream converts every input signal, both PCM and DSD, to single-bit, high sample rate 20X DSD signal. Use of a FPGA rather than an off the shelf DAC chip provides immense processing power, resulting in complete lack of digital glare, and allows the owner to download OS updates as they are released.

@mitchb My latest Auralic product (Altair 2.2) refreshes firmware on every reboot. Which is a great feature for those of us who aren’t always paying attention to the latest updates.
I think you are implementing best practices by rebooting, especially by hard rebooting by which you are resetting the hardware. If nothing else, it should help reset digital voltage levels to valid ‘High’ and ‘Low’ levels; they can get hung up at levels that are neither fully ‘On’ or ‘Off’ and generally restrict communication. I can recall having to drop power at both ends of a serial RS232 link in order to restore communication over some relatively long line links (200+ ft). I imagine the same limitations apply even in a high speed chassis as found in modern DACs, but I could be wrong. I just think you may not be imagining things, but as other contributors have suggested, the matter deserves further investigation. 

Seems spurious unless you flush cache in the process. Normally though cache sits in the streamer, not the Dac. And restarting the clock is generally deemed highly counterproductic because of destabilisation.Either way, if it works keep doing it.