Very true on the large crossovers. When I initially did my speakers, I did the Kicker KSS690 running off of the stock B&O. I had some of the small inline kicker crossovers left over from a previous install & used those for the tweeters.
Do not skip the crossover for the tweeters. The stock tweeters, be it B&O or non, have a capacitor built in to the tweeter itself to limit the lower frequencies.