I just got my SMSL M8 - just hooked it up - it is pretty close to my iFi Nano but the output on the SMSL is higher. I didn't buy the P1 PS but I may try it at a later date. I did get the newer M8 as there was a BIOS update just after Jan 2016.
The firmware update added "screensaver" to the diaplay...turns off the OLED if it hasn't updated status in a while. That happens when samplerates change or you start or stop DSD playback. It was a relatively minor update.
The new M8 handles up to 768khz PCM.