Stevecham, Life is not that simple. Based on your logic, every speaker designer should use 6db slope crossovers, and any design not using them is inherently inferior. That's just not correct. A speaker can sound very good (or bad) using either first-order or sharper slope crossovers. That aspect alone doesn't tell the whole story.
It is true that first-order (6 db) crossovers have a mathematically ideal performance, i.e. the frequency and phase response of the two drivers will add mathematically to a flat frequency and perfect phase response. Other types can come close but are not textbook perfect. However, there are other considerations. A first-order crossover makes greater demands on the out-of-band performance of the drivers. Each driver needs to have smooth response for at least two octaves beyond the nominal crossover frequency. Also, the driver must be able to handle high levels of power beyond the crossover frequency since there will still be high signal levels there. These factors limit the drivers that can be used with a 6db crossover.
In addition, a speaker with first-order crossovers has more pronounced lobing. It's easy to hear this by simply moving your head up or down vertically while about 3 feet away from the speaker. There will be significant peaks and valleys in the response due to lobing. This effect can be averaged out by being further away from the speaker, and it also bothers some listeners more than others. I found it quite annoying when I owned Thiel 3.6 speakers.
I have used first-order crossovers on many speakers (including the Thiel 3.6's that I owned for about 10 years), yet my speakers now all use sharper slope crossovers for the simple reason that they sound better with my particular drivers.
With regard to the midrange driver being connected out of phase, this is the proper means of connecting a driver to a second-order (12db) crossover to get the optimal response due to the phase shifting that occurs with the crossover itself.
As far as the OP's question is concerned, I have no opinion since I haven't heard the CS6. I have heard the Sophia 3 and the Sasha several times recently and they are certainly very good sounding speakers whatever crossover slope they may have.
It is true that first-order (6 db) crossovers have a mathematically ideal performance, i.e. the frequency and phase response of the two drivers will add mathematically to a flat frequency and perfect phase response. Other types can come close but are not textbook perfect. However, there are other considerations. A first-order crossover makes greater demands on the out-of-band performance of the drivers. Each driver needs to have smooth response for at least two octaves beyond the nominal crossover frequency. Also, the driver must be able to handle high levels of power beyond the crossover frequency since there will still be high signal levels there. These factors limit the drivers that can be used with a 6db crossover.
In addition, a speaker with first-order crossovers has more pronounced lobing. It's easy to hear this by simply moving your head up or down vertically while about 3 feet away from the speaker. There will be significant peaks and valleys in the response due to lobing. This effect can be averaged out by being further away from the speaker, and it also bothers some listeners more than others. I found it quite annoying when I owned Thiel 3.6 speakers.
I have used first-order crossovers on many speakers (including the Thiel 3.6's that I owned for about 10 years), yet my speakers now all use sharper slope crossovers for the simple reason that they sound better with my particular drivers.
With regard to the midrange driver being connected out of phase, this is the proper means of connecting a driver to a second-order (12db) crossover to get the optimal response due to the phase shifting that occurs with the crossover itself.
As far as the OP's question is concerned, I have no opinion since I haven't heard the CS6. I have heard the Sophia 3 and the Sasha several times recently and they are certainly very good sounding speakers whatever crossover slope they may have.