One Monoblock or Two?

If you bi-amp, you probably don't want 2 - 300 watt amps instead of one 600 watt amp. The high frequencies need much less power than the lows, so it usually makes more sense to use a fairly large brute force amp on the bass half, and a much smaller but hopefully higher quality amp on the treble half (finesse!).

The details depend on speaker specifics, but a simple down the middle split you describe will waste a lot of amplifier. The unused reserves of the large amp on the treble side are not available for peaks on the bass side. The treble amp loafs while the bass amp works hard.

A better split might be 300-400 watts on the bottom and 30-40 watts on the top. Again, the devil is in the details and this should not be taken as a recipe.

You also have to consider gain matching of the amps, unless you use an active crossover (recommended). If you use an active crossover you will also want to bypass the speaker's passive crossovers if possible. This of course opens other cans of worms....

You also need to consider the sonic signatures of the amps used on the top and the bottom. It's safer to stick with the same brand line, but you can sometimes get great results by breaking that rule. A low powered tube amp on the top combined with a large solid state amp on the bottom sometimes works well.

You will have years of audiophile nervosa ahead of you!

Ghost, instead of saying.....how much power is needed per 'half', I'd have asked what the crossover frequency was.

The 50:50 power point is about 350hz while more power is indeed needed by the lows as crossover goes to higher frequencies.

Also, I think it is just possible that amps have different latencies...That is, the amount of time it takes for a signal to go from inputs to speaker. Even very small differences will result in phase shift near the crosover.

And as a final point, I'd agree that Active crossovers would really open up a can of worms, but if I had deep pockets, that's the way I'd head and start with as close to the 'stock' transfer function as reasonable.

Again, please look at the biamp link I provided. Good stuff:

For Infinity, don't bother with an active crossover. Sure, the DIY'er in me is curious but, instead, stepped up to Genesis, which already has all that.

BTW, there's a Genesis V listed in the Chicago area (local pickup only) for $1200.

"First, what do you call a 'difficult load'? "

- High values of "Equivalent Peak Dissipation Resistance" or EPDR which is, simply, the resistive load that would give rise to the same peak power device dissipation as the speaker itself. Using EPDR as a figure of merit, the speakers can be compared directly with each other.

"The high frequencies need much less power than the lows,"

It is correct assumption with some speakers and wrong with others. For example, most of electrastatic speakers high
frequencies required 7-15 times more of EPDR (see above for definition) then low frequencies.

All The Best
Simon

EPDR takes into account the reactance of the load.
My preference is to go to 'root' and use powerfactor. I also like the power cube way of measuring amp output by taxing the amp with inductive, capactive and resistive loads from 1->8 ohms, and +-60 degrees.....You measure the extremes and the amp is good 'under' the limits measured. The graphic gives a response range for the amp which is intuitive and easy to understand.

Electrostats may just be a wacky hi phase load at higher frequencies. Fortunately, those frequencies in normal music require the least power.

http://www.audiograph.se/Downloads/PowerCube_12p_brochure_complete.pdf

Also, most speakers when measured (why bother? seems to be the attitude) are only measured for impedance, which from the above and EPDR, is only part of the story.
I have been a big fan of a different presentation of the same data in the form of the Smith Chart.
I understand the RF guys like this.(microwave?)
Anyway, it also, when scaled properly, makes perfect sense for speakers, as well.

The 50:50 point for power is AROUND 350 hz, based not on speaker need, which you can't know in advance..or predict for YOUR speakers, but simply on acoustic power. Add more as you see fit, based on how wacky the speaker load is.

What got me thinking about this was a long time ago, the original Braun Tri-amps which had 100 watts RMS per speaker divided 50:35:15 with unknown (to me) crossovers.

Article on the Smith Chart presentation.
http://www.hometheaterhifi.com/component/content/article/228.html