12 dbs passive crossovers have the same problems. If no time alignment is used, great results can be had by simply swapping the polarity on the mids, and leaving the sub and tweeters congruent with each other. If T/A is used, this may need to change. I had my sub the same as my tweeters until I delayed my whole front stage 4 feet. Then it became necessary to swap the polarity of my sub, and then I had up front bass as intended. I'm using an analog active crossover.the main problem that people have with active setups is getting phase mixed up. this is because at 12dB/oct and 18dB/oct slopes the speaker has a 180deg phase shift. this is the same as reversing polarity on the speaker. you need to keep careful track of that as it relates to mid - tweet and woofer - mid combinations.
"hollow" sounding systems are usually suffering several forms of phase interference. see my build log to get an idea of how i install speakers.
Isn't it true that DIGITAL crossovers (DSP) are able to circumvent the phase problems of analog crossovers (whether passive or active)?