I did that with my Infinity RSIIb's and it sounds excellent. An external crossover allows you to use much larger (better) components and to space them well apart to prevent crosstalk interference between crossover components and between the crossover and the speaker magnets. Here is a picture with the crossover box open:
External Crossover
and here is another picture of the system:
RSIIb Speakers
.
External Crossover
and here is another picture of the system:
RSIIb Speakers
.