Recommendations for electronic crossover.

God idea. 
At best having to bridge an amp is poor planning. I think the best posts her on the subject of biamping  are by mijostyn and avanti1960. If you are making your own speakers and want to approach the problem of a 2 or 3 way system that way there are certainly advantages. Bypassing the cross over network of a well designed  speaker made by a reputable company is a mistake unless the speaker was designed for it. 

Arguing about whether bridging is good or bad misses the point. Many base designs (such as those from Nelson Pass) are bridged inherently. They allow the use of lower power supply rail voltages and therefor reduce power consumption, particularly with Class A configurations. I don't think that a properly designed bridging configuration increases distortion any more than using fully balanced circuitry does. It is true that each amplifier that is bridged will see half the load impedance, and as such must be designed to drive that lower impedance.

Regarding the subject of active XOs, it is almost impossible to find one that is built without op amps. Bryston is the only company that comes to mind that produced HP and LP versions with discrete Class A circuitry, and I do not recall if these are still in current production. In any case they are not cheap, and if you need more than just a single XO point (two way system), the costs mount up fast.

For the poster who mentioned potential pitfalls of eliminating the factory passive XOs, almost all of these are removed by providing a dedicated amp/driver. Line levels are easy to match with gain controls on the amps, and most other impedance matching gymnastics are eliminated with a dedicated amp. The system is also much more efficient if the drivers have widely different sensitivities, because you do not have volume matching resistors wasting a lot of power. The passive components are a lot cheaper and you can use higher quality. For example, teflon film caps are almost impossible to get (or afford) as large values in a passive XO, but are affordable in an active design where they are a lot smaller in value. For more discussion on the advantages of dedicated amping, see Professor Linkwitz discussion on the matter.

@dhl93449

Regarding the subject of active XOs, it is almost impossible to find one that is built without op amps. Bryston is the only company that comes to mind that produced HP and LP versions with discrete Class A circuitry, and I do not recall if these are still in current production. In any case they are not cheap, and if you need more than just a single XO point (two way system), the costs mount up fast.

This stance is a quick way to discard active XO’s when in fact they could be beneficial to a passive solution - even with opamps and A/D to D/A conversion being introduced in the signal chain.

What’s the bigger picture; do the comparison and forget for a while the drawbacks mentioned to hinder the fuller realization of an active XO, if they’d even be that relevant compared to the negatives of a passive config., and then see. My take with an XP-series Xilica XO is that it trumps excellent passive XO’s in the three set-ups I’ve heard so far - quite easily. The sound in all cases went from slightly diffuse/smeared and soft to more clear, refined, transparent and dynamic going from passive to active.

I have successfully used the DriveRack dbx PA2 LMS (loudspeaker management system) with vintage gear and some modern speakers. It works quite well as an external xover for 2-way and 3-way speakers and is affordable. The only downside is that it requires some time and patience to setup and it looks like Pro gear (which it is) and not home audio gear. I mount it backwards in my audio rack and it's practically invisible.

Audio Nirvana published a great article about restoring vintage Altec Lansing Model 14s and described how they used this box to overcome some fundamental design flaws of the 14s. I followed their recommendations and it works great. Here's a link: dbx DriveRack PA2: The Future of Audiophile Systems

Although I don't find external EQ and xover to be necessary in most situations it has always improved the sound of whatever speakers/rooms I have used it.