Hola: Ethos model is a small version of the Montis. Difference? With the Montis, everything is done without effort. Wide stage, deeper sense of 3D, better bass, it challenges his big brother, the Summit X in many ways. I am not saying that the Montis is better than the Summit X, what I am saying is, for a smaller room, Montis will bring out effortless what the Summit X does in a big room. The stat panel is exact, but only one 10" woofer on the Montis. So, the difference is there, at the bass energy.
Getting back to the Ethos, it uses the same power amplifier built in the Montis, but a front firing active 8" woofer and a passive radiator firing to the floor. This array gives to the Ethos deeper bass than the Ethos replacement model, the Vantage, but not as good as the Montis.
The woofer integration of the Montis it's almost perfect. The Ethos fails the clarity and the quality of the bass if you do a comparison between them. But, let me tell you that the Ethos is a very good sounding speaker too.
Because both speakers have the Martin Logan magic, I could live with both, but Ethos is only a step backward. Both shine with the music, and brings the musician(s) playing for you, there, in your room, but Montis goes ahead doing it effortless. The cymbals are projected with tons of space, with the right timbre. Metals are clear and crispy. Percussion has a lot of dynamics, on both models. Vocals are better on the Montis.
I do believe that, if you want a better sounding Ethos, which is one of the best speakers available at its price range, get the Montis. Quality has no regret!. And Montis brings wider stage, and with having bigger stat panel, the reproduction of the musical instruments are more transparent, with better bass quality. The definition of the bass notes are breath taking.
Montis is the way to go, definitively.