Two Stereo Amps, Bi-amp or Monoblock?

From what I have seen, the normal step-up from a bridgeable stereo amp is to buy another and use them in monoblock format. You could however buy another and leave them in stereo and simply use one amp for both channel tweeters and one amp for both channel woofer/midrange. I understand that this is not a full 4 monoblock bi-amp configuration, but I wonder if the bi-amp advantage is glimpsed to a large extent in this format and perhaps a better sonic improvement over running the two amps in monoblock. Thoughts or experiences? Aside from sonic benefits of either, what is the resulting power increase from the two formats? In the "bi-amp" format you would also have the ability (or advantage) to offer a different amp to the tweeters and to the woofer/midrange; whereas in the monoblock you would need to match the amps.
Sometimes bridged amps are thermally or other wise limited in thier ability to offer double their stereo capabilites in mono configuration.
Bi-amping is almost always better than bridging for several reasons.

1) If you bridge into mono you typically do not double current output, but the rated watts RMS may double. This ought to give you an indication of how relatively meaningless watts RMS is to begin with, but the real point here is that you will not be using amplifier power as efficiently as if you bi-amp in which case you will be doubling your current output.

2) Related to the above, but also important in and of itself is the fact that many speakers have demanding impedance loads, often times in the bass frequencies. If you bi-amp, you are providing two isolated amplifiers, one to the bass, and one to the highs. When the bass drops impedance and pulls large amounts of current from the amplifier, the amp hooked up to the highs does not see this load and is unaffected. The result is that whereas if you had been running one bridged amp you might have been running out of current and shutting down the highs and mids when the bass kicked in, now you are preserving highs and mids regardless of what the bass is doing.

For these two reasons, especially on speakers which present a difficult load, I always recommend bi-amping.
Bi amping is better as mentioned above, you have an amp that does not see the power supply killing low frequencies, and can run free of the effects of IM distortion. The amp on top is allowed to deliver it max sonic potential basically free of clipping.

Also from what I have read elsewhere when you turn a stereo amp into a mono amp the amp will not sound as good.
Thanks for the response. I sent this question to Steve Deckert of Decware (zen amp) and he replied:

"The pros of use as monoblocks is 3dB more power before clipping, and better separation. Also the ability to place each amp close to the speaker so you can use less speaker wire.

The pros of biamping is the ability to adjust the volume of the tweeters and woofers separately. Also allows you to voice each amp to more ideally compliment the signature of each driver."

I'm gathering that biamping with stereo (2 total amps) does not increase the power while biamping with mono (4 total amps) would.

Anybody have experience running Zen amps on De Capos in any of these configurations? I guess I'm concerned about the medium efficiency (92db) for a 2A3
I went through this bridged/biamping decision within the last few months. I had started by bridging my two Rotel 980BX's into a pair of Totem Rokk's. Obviously I didn't need the power for these speakers, but I wanted to see what difference shortening the speaker leads would make. I started with an old shotgun set of 10' XLO cables and clipped them down until I had about 4, 18" leads. I could distinctly hear an improvement in the details of the music.
Not long ago I swapped out the Rokk's for a pair of Aerial 10t's. These do need the power, but more importantly, they need the current. So after a few hours of listening at modest volume levels, I switched back to stereo mode and horizontally biamped which required using the other 7' of the XLO's. The details were still there, the bass improved, and I can turn up the volume more without the fear of clipping and damaging the 10t, which are worth far more than the amps.
What about true Monoblock?..Do they sound better then bi-amping?..For instance, would bi-amping 2 Pass Lab X350 or X250 sounded better than the 2 mono block of X600?

Long, one can bi-amp with 4 mono amps. I think it depends on your speakers and what your goals are. If your looking for greater dynamics or volume, more power might be better. If you have speakers with large impedance swings and your looking for cleaner sound, bi-amping with smaller amps might be better. These recommmendations are used with built in cross-overs in mind. Bi-amping with active crossovers (assuming of course that the active cross-overs are of equal or better quality than the built in passive ones they are replacing) should provide an increase in dynamics as well as cleaner sound. Of course you can go for broke and use 4 big mono amps with superior(?) active cross-overs. This is of course based on the assumption that you are using a 2 way speaker system. Ideally every driver would have it's own dedicated amp.