did you listen to both models in the same room ?
That would not be possible since one is being sold at Archi Audio and the other at Spectra, but both stores didnt really have a big difference in their room displays. I had about 30 mins gap listening to the 2 speakers, so my comparison was memory based and not AB test in the same room.
Aside from the room, other factors have to be considered like the gears used, etc. But like I said, my observation is based on my listening preference.
There was a guy there who was about to buy EPOS speakers but when he heard the M51 w/ me, he changed his mind, lol.