Bi-amping LF with high-powered pro amplifiers

The real question here is, how compatible will the bass amp be with your existing amp? If you are going to biamp it is better to use the same amplifiers so you do not here a change in character at the crucial crossover point. There are some exceptions to the rule such as subwoofers with a built in amplifier connected directly to the main amp via the amplifier outputs. Using this method the subwoofer amp will take on the character of the main amp while receiving a sample signal.

I bi-amp the low frequencies with a pair of Rowland 201s and a Model 10 on top. I use a Rane equalizer as an external cross-over to shape the sound to the room. The bass is rich and deep and does not suffer from any of the anomolies of digital amps used in other applications. I firmly believe that this combination out performs any conventional amp in the same price range.

Yeap...done many a time by many a peoples.
I currently use a Crown XTi my bass drivers. The Crown has a DSP with electronic crossover, EQ, delay, etc.
500W into 4ohms.
I use a tube amp on my mid/hi drivers (320Hz and up)

The issue Rrog raises is real but it may come down to whether the crossover point is low enough to avoid any soundstaging or tonal disparities between the 2 amps. If near 100hz or so it shouldn't be any big deal, but much above 200hz or so and things could start to get dicey, depending on the degree of disparity in sound. Also it may be a question of macro dynamics, but it may also come down to roughly the same frequency range I mention - just as long as the specs for each amp don't point to a major difference in dynamics between the 2 amps. And you just use some common sense, too, I think: I wouldn't try to mate a 400-million watt class D amp with an 8-watt tube amp with a wooly-sounding mid-bass or anything like that - but, that's not to say that I think this idea can't end up working pretty dang well, actually. I'm considering this move for myself down the road when I can afford it in total (looking at Behringer Inuke currently). You may prefer the high-level inputs going into the pro amp for a bit better sound quality if your main amp already has 2 pairs of speaker outputs. If you've only got 1 pair, the single-ended inputs will do. If your system is balanced, then you'll have to make for yourself what nobody sells: a balanced Y-adapter! That's the boat I'm currently in.