What is the scoop on passive biamping?

Picked up an HK Cit 12, recently, which I intend eventually up to mate with an Advent 300 in my second system. But I am curious about biamping with it.
Would like to try driving my Tower IIs with the 12 up top and my regular Adcom amp for the bass. The speakers are set up for biwiring or biamping but I have no crossover to insert between my preamp and the amps.
Is it wise to hook up in this way? Is it recommended? What can I expect?
You'll need one of your amps to have adjustable gain, as it is highly unlikely they will match.
Second Inscrutable's comments; my suggestion is to look at Bryston's Pro amps, they have such a feature, and they are excellent SS amps.
I have four Marantz MA-700 passively biamped to Boston Acoustics VR30's in my modest system. It works great. Have also just purchased a set of Infinity Modulus speakers with servo sub and electronic crossover (1990 vintage) and am anxious to see how they work in my system.