Actually an easy way to actively bi-amp your Aerius's is to add a sub woofer with its own amp and a high pass x-over that is worth a damn (Like the Velodyne FSR/HGS series of one from HSU). By rolling off the bottom end of the ML below 50-80 HZ, you will pick up a nice amount of headroom on both the main amp & MLs, add extension down to 20HZ, and considerably open up the soundstaging of the MLs to boot. A brand new Velodyne FSR-12 sub can be had for $800-900. You can get more options by going to an outboard active electronic x-over (Marchand or HSU). This allows you to expand your choice of subs to those that are excellent (REL for example) but don't have high pass filters built into their electronic x-overs.
Bi-amping advice for M/L Aerius
I am interested in bi-amping my M/L Aerius. They presently are running off a B&K Ref 2220. Would my best be to get another 2220; or could anyone recommend another amp that would match it well?