Since I have built open baffles, I have never thought about upgrading speakers. All I am experimenting with the tweeter. I recently changed the Piezos to
Iwai silk domes. these are tiny ones but provide better high frequency
Iwai Electronics Pvt. Ltd.
Since they have given nominal impedance to be 6 ohms, I tried 3.3 MicroF caps so that I get 1st order high pass filter somewhere around 8khz but the sound was not pleasing. So i studied the impedance graph again. It seemed that the frequency where I intend to use the tweeters has impedance at about 4 ohms. obvisouly, for 4 ohm, the 3.3uf works as high pass filter at 12kHz. I do not have frequ response curve generator but I am sure it would have shown big dip between 9Khz and 12KHz.
So now I needed 5 microF capacitor. I also wanted to try something different than electrolytics. I decided to go ahead with MPP caps used on fans. The only sterngth available was 2.5microF. So I put 2 caps in parallel to achieve 5microF value. Now this gave me great sound. Better than the Piezos and 4.7microF electrolytics. The Frequency response curves and impedance curves of drivers help quite a lot in choosing the right compoonents.
Somewhere I read that MPP caps are better than electrolytics but are comparitively very big. With big open baffle speakers, who cares about the size?
I have also changed my soundcard from onboard to Asus Xonar DG. At present I am using its optical out to feed my DAC. Yet to try its analogue out. Will do it once I get my preamp (expected to get it by Monday). Will start a new therad about all the recent changes that i have made to my system.
The small active XO in the link that you have provided has XO frequency from 50Hz to 2.5KHz. Not useful for me because I need it to be about 8KHZ.