I think one of the major advantages to bi-amping is using different amps: each with their own qualities to add to the mix. I know this runs counter to many people's opinions, but what the heck. This is mine.
Here's the deal. I designed the active woofer systems for several loudspeaker companies and in each case I made sure the power amp module for that active woofer section was designed specifically for the application. I designed an amplifier that I would never suggest using on a full range loudspeaker, yet it's wonderful for the application at hand. I have also assembled bi-amped system using a delicate tube for the top end and a brute for the bottom with great results.
This practice isn't for the faint of heart. Matching levels and characteristics is only the first part of the problem, as we've discussed in earlier posts. The crossover is critical as well. I've used a derived analog crossover like those John Curl designed in the Symmetry crossover, intending to give perfect phase response, and had good success. I've also designed sloppy 6 and 12dB/octave passive filters with great success as well.
I guess the point of this is simple. If you're going to go to the trouble of bi-amping you might as well go for the gusto and add an amp that glorifies the particular region of sound you're trying to reproduce. In its simplest form, you can place a pot (attenuator) on the louder of the two amplifiers and, using a sine wave generator and a voltmeter, match levels pretty close to each other. Then you need only a crossover. Here I would shy away from active crossovers as you're adding a whole new layer of grit and problems you probably don't need. Remember, a passive crossover inside the loudspeaker is usually nothing more than a handful of caps, resistors and coils of wire.
You can better and more easily duplicate the same slopes as an internal crossover if you do it externally and with much better parts. For example, the impedance of a driver is typically 4 or 8 Ohms. This necessitates a very large cap and this, in turn, means the quality of the cap goes down as the size goes up. The typical input impedance of a power amp is 10,000 times higher, so the size of the cap can be 10,000 times smaller. As the size of the cap goes down the quality goes up.
These are just some ramblings about why I would either go for the gold with bi-amping or stick with bi-wiring if it looks to be too much of a task.
And, if you're like me in my quest for simplicity, you'll just get the very best cables you can, run a couple of monoblocks and call it good.
