Active Subwoofer Crossover

I've tried several different crossovers - some active and some passive.  the best sounding, and most flexible, i've found is the XTA DP-224.  one feature in particular that i found has made a significant difference is the ability to time delay the mains.  once the crossover and delays are dialed in, the integration between the sub and mains is absolutely seamless - better even than the vandersteen system, in which the HP filter and the sub amps are purpose built to provide a seamless interaction.

Glad to hear about your decision.  Keep experimenting with the crossover frequency.  80 Hz was really just a starting point, as you discovered.  Room nodes may also play a part in where you finally end up.

"one feature in particular that i found has made a significant difference is the ability to time delay the mains. once the crossover and delays are dialed in, the integration between the sub and mains is absolutely seamless".

"I’ve changed the crossover to 45 hertz and like the overall sound better".

+1 to both.

Also, a 45 Hz crossover means that bass can be separately adjusted if needed, say, for a particular recording, without unduly affecting the chestiness of male vocals or other lower-midrange sounds.

I've found more flexibility, with subwoofer crossovers in particular, to be key. Pretty difficult to overrate in an ideal setup, let alone in anything like a problem room or with unusual gear. 
Cheers.

Keep in mind, the only way your amps can ever communicate directly with your speakers is with an external crossover.  With an internal crosover, your amps communicate with the crossover.  With an external crossover, there is nothing between the amps and speakers except speaker wire.   

I thought setting the crossover to 80 hertz was considered optimal? How do you establish the correct phase?