I haven't compared the two but I do own the Plinius M8. It is a very musical preamp that provides very good detail, without sounding gritty or harsh. While it is ss and not tubed, I find its sound to be very liquid and organic - certainly not typical of ss.
It's one weakness is that the very lowest bass. It isn't out of proportion with the rest of the spectrum or non-existent, but rather, it isn't quite as strong and dynamic as some of the best preamps out there. Again, this area isn't bad in any way, just not the best I have heard and not quite as good as its outstanding mid-range and highs.
I am using a tubed source (Modwright Transporter), tube amps (Atma-Sphere MA-1's), and Vandy 5A's with the M8 and it really works well and is not out of place with the more expensive gear in the system.
While Plinius is known for their amps, I think this preamp is a sleeper product and might represent their best value proposition.
I highly recommend that you try to audition one and see if it works as well for you as it does for me.