Biamping and subwoofers....

What Alnan describes certainly works, it's a little extra expensive and you must get "inside" your main speakers to bypass their internal crossovers. Many will argue that this is the preferred way to do it.

There is at least one other. I'm assuming that your application is simply 2-channel. Bi-amp the mains as you normally would. Run another pair of speaker cables from the left amp another from the right amp (only using one channel on each to the HIGH (speaker) level inputs of the sub. The impedence of these inputs is so high (~100k ohms) that the amplifier will never know you connected the sub.

Check out the REL web site. It has some detailed hook-up info on it.

I think your sub would have to go too high to do it by biamping. Here's how I do my system(although someone might have a better way): I biamp my main speakers with an electronic X-over, and run a separate line out signal(which is full range) to my Velodyne sub. I turn the crossover on the sub to minimum (which is 40hz on my Velodyne)and then raise the volume on the sub until it sounds like I like it. Works for me, although there might be a bit of overlap on the bass, depending on how low your mains can go. Biamping is the only way to fly! If you need more info on my system, e-mail me and I'll give you particulars. Good luck.