If you've already built this 2-way, I wonder if you'll really want to change things, but we can always discuss ideas.
The biggest problem I see is trying to get both more bass output and extended high frequency range from a 10" driver. You can't have it both ways without something suffering. You may have measured a frequency response (FR) as high as 4000 Hz, but a FR curve only tells you how loud the sound is at a given frequency. It won't tell you if the speaker is in break-up mode making unwanted noise.
In this FR curve, look in the 2,000 to 5,000 Hz range. There is a sudden drop of nearly 10 dB in response just below 2,300 Hz, followed by a rapid climb by nearly 20 dB by 3,300 Hz. Above that frequency, there is a steady drop off in response. This is characteristic of a paper coned driver in break-up mode, and suggests (but does not conclusively demonstrate) that's the Beyma 10" is also doing that. The rapid up and down swings seen the harmonic distortion curves between 800 and 4,000 Hz also suggest something unwanted may be going on.
The sound may be as loud in the 4,000-5,000 Hz range as it is below 1,000 Hz, but it will not be smooth sounding. At lower volumes this may contribute to an apparent increased detail over and above what's in the recording. Do brass trumpets or horns sound more detailed or more forward? Some people may at first like this increased edge in the upper mid range/lower treble. If you increase the volume, do the brass horns or trumpets sound too forward or become fatiguing? This will vary with the type of music or sound. You have to have a signal that produces those frequencies to stimulate that response.
I wonder if a 2nd order low-pass filter at 2,300 Hz will effectively suppress the break up noise. You can try using a lower crossover frequency, using steeper roll-off slopes, or adding an LCR trap filter to suppress the noisy frequencies.
And then there is the problem of beaming, but I already mentioned that.
Dennis Murphy is a self taught crossover designer with over 25 years experience. He has designed most of the Salk speakers, all the DIY designs at Murphy Blaster Productions, and more recently all of the Philharmonic Audio speakers. Over the years, I have become familiar with his speaker designs, and I've learned that I like his design taste and philosophy. In particular, he favors a flat FR curve over as wide a range as possible. He also depends on his own accurate measurements as a necessary step in crossover design. He has successfully used a variety of 2nd, 3rd, and 4th order crossovers, and is not wedded to a single type. He also makes the distinction between a crossover's electrical performance and roll-off curves, and the acoustic roll-off of a driver combined with the crossover. What matters is the acoustic performance. He has very rarely (or never) seen a successful speaker with a simple 1st order (electrical) crossover. There are some good commercial designs such as Vandersteen, that tout 1st order crossovers, but a quick look at them reveals that they are far from simple minimalist crossovers.
Baffle step compensation (BSC) is not so much a matter of preference as it is based on knowledge of how close a speaker cabinet will be placed to the wall behind it. The further away from the wall, the more BSC is needed to maintain a flat FR curve. In your 2-way speaker with a 6½" woofer, did you use BSC or avoid it to keep the sensitivity higher?
Others may have different opinions than mine
Zaph Audio's driver tests are a very good source of info and his measurements are widely considered as reliable.
The other web site you mentioned (http://www.mh-audio.nl/index.asp
) has "textbook" calculators for crossovers, but you mentioned how you've already observed how small changes in components have unexpected effects on the the rest of the crossover, such as in the notch filters. The trouble with the crossover calculators based on "textbook" values, is that they assume driver impedance is constant across the bandwidth.
Yes, I agree, there is much to learn in this hobby