Either way, passive or active, you have to decide if you want seams or holes in your system response or whether you want it "tunable" with an active crossover. As mentioned previously, if you can remove the passive built-in crossover easily from your speaker, then, since you plan on spending some serious money on amps, I would imagine that an active crossover isn't outside your price rance, then definitely go for active. If you don't want active, then you would need amps of equal specifications or the same amps. otherwise you definitely will have seams that you will notice. So, after all the posts, the choices are really simple. Active, you can get different amps for low/high and adjust with the crossover. solid state for the low and tube for high depending on your listening desires. Passive, you get the same amps for high/low or amps that are pretty close in specifications and you are good to go. It really isn't rocket science. It is only complicated if you allow it to be. You have two choices.
If you can easily remove the passive crossover, like my Martin Logan Monolith III's it is simple to remove them, since they are external passive crossovers and insert an active crossover to the system (which is what I did), and borrow an active crossover and amps and experiment to make your decision. I am a strong believer that when one is paying a large amount of cash for this type of equipment, borrow equipment first and take it home, insert it into your system and hear how it sounds in your system before purchasing. Asking others for their opinion is okay, however, that is what it is, their opinion. Your's is the only one that matters.
Find good dealers and stores that will allow you to take equipment home for a home demo first. They will have used/consignment/demo equipment or new equipment and take your credit card info. give you the equipment for a week or so and allow you to make an educated decision based on home listening.
Also, get on-line and check. I would bet that there are some active crossovers out there specifically designed for your speakers.
enjoy
