2 stereo amps in a mono-block config = 2 x power?

I wish to double the power of my system. I have a stereo integrated amp with two sets of pre-outs. One set of pre-outs is connected to my sub. The amp manufacturer offers the power amp portion in my integrated as a stand-alone stereo power amp. If I drive one channel with my integrated, and connect the other channel via one pre-out into one channel of the stand-alone, will I effectively be doubling my power? I cannot bi-amp in the traditional sense, as my speakers have only one set of binding posts. Also, by keeping the one interconnect to the stand-alone amp as short as possible, will I be introducing problems with coherency between the two speakers (time and phase) or cause other problems?
Unless both pwr. amps are the same, the sonic signature will differ so bye bye coherence.
Pre amp "out" signals are usually 2 volts or less. Your power output of the amp would be the rating of the amp. Are you talking about 2 separate compontents when you say the "manufacturer offers"?
It sounds like you want to connect the preamp "out" of your integrated to the preamp "in" on the same unit? Maybe I missed something.
I can't visualize your set up--do you just have the integrated with two stereo amps built in, or do you have an integrated with a stereo amp built in and a separate, standalone power amp? In either event, going from two stereo amps to two mono amps with twice the power is not always possible--stereo amps have to be "bridgeable" to do that, and its something that most amp manufacturers don't build in...
My setup is: I own a stereo integrated amp rated at 90wpc into 8 ohms. My speakers require more power than my integrated can adequately deliver at higher volumes. My intent was to buy a new separate power amp to connect to the pre-outs of my integrated so I could at least utilize the pre-amp section of the integrated, saving myself the expense of replacing it with a separate pre-amp. I asked the distributor of my integrated for pre-out specs so I could properly match it to a new separate power amp (I've read that the power amp input impedance should be at least 10k times that of the pre-amp output impedance). But instead of providing the requested specs, he suggested I purchase a new stereo power amp from him. One which is an exact duplicate as the power amp section in my integrated. Then use the two stereo amps (one stereo integrated and one stereo power amp) in a monoblock configuration: one channel from the stereo integrated amp dedicated to one speaker; and one channel from the separate stereo power amp dedicated to the other speaker - so each channel is driven by a different amp. He suggested that would provide each channel with 180 watts of power into 8 ohms, since only one channel was being loaded per amp. Is this clearer?
No, you'll still get only 90w per channel with the setup you describe, though having an extra power supply may make things sound a bit better. Not using one of the channels doesn't double the power rating of the remaining channel.

If you want more power you'll have to replace the integrated.
If the integrated's internal amp's two channels can be bridged into one channel driven by one of the integrated's preamp channels, then yes, you can benefit from more power as a single channel amp here. I highly doubt the integrated has such a feature....but you never know. Maybe there are jumpers in the unit to provide this.

If the above is possible, you have one channel down, one to go. The problem now is to find another amp with exactly the same sonics as the newly bridged amp in the integrated. This is even less likely than the bridging option to begin with. The last thing you want to do is drive the speakers with "different" amps. And yes, the one IC to the external amp would certainly botch up the match between the two channels even if the two amps were the "same". And locking yourself into an amp that matches the one in the integrated is simply too limiting. This is a goofy proposition all the way.

I would consider any number of other possibilities before I went through the pain of what you have proposed:

1: If you want to upgrade a little at a time, find an amp that will drive your speakers to the musicality that you desire. I suspect that the integrated's preamp section will drive all but the lowest sensitive amps (typically matched with high output tube preamps) just fine.

2: Ultimately determine which is more important to you, the speaker or the integrated, and look to find a more suitable mate to the piece you decide to keep.

3: It looks like you are using a subwoofer. Is this not buying you a lot of headroom for the amp in the integrated to give the presentation more dynamics, control and slam? If you are driving the main speakers full range, perhaps you can crossover the speakers with a high pass filter as the sub is handling the bottom 2 octaves or so. This would free up a lot for the amp to more easily drive the the remaining frequencies in the main speakers.

4: Investigate other reasons why you do not have the dynamics and/or control in the sound that you anticipate is lacking now. As my sources have become more refined and resolving, I find that I play the music lower in volume.

Hope this gives you some ideas to consider.

John - Thank you for the detailed explanation. It is much help. The proposition sounded goofy to me too. I cannot insert an external crossover for my mains as my integrated does not have any power inputs, therefore the mains run full-range. I am pleased with the dynamics of my system and usually do not require higher volumes. But sometimes I do, like when I play rock. So it would be nice to have some extra power on occasion.
The second (power) amp is a duplicate of the power section that is in my integrated.
As you suggested, I think I'll be better off just getting a more desireable power amp. A new power amp would then also provide the capability of inserting a crossover to ease the demand of my main speakers. Thanks again.
And just for the record ... I misunderstood my dealer's suggestion completely! A follow-up contact with him revealed that he meant for me to simply bi-amp my speakers (which I cannot do since my speakers have only one set of binding posts). So all of this confusion was for not. I am the Mayor of Stupidville. And for my punishment I will dump my current system and get a Bose Wave Radio ;>}
Now, now - the crime wasn't that bad!! Bose is the audiophile death penalty.
Dan, there's lots of misinformation here and some good advice from John. But allow me to again* explain paralleling and bridging amplifier channels.

Connecting the stereo amp's positive binding posts together and the negative terminals** together and driving the 2 channels with the same signal is called paralleling. The now-single-channel amp has the combined power, in your case 180 Watts, and it's TWICE as capable of driving low-impedance loads. For instance, a SS amp that's rated at 90WPC into 8 Ohms will be able to drive 180 Watts into 4 Ohms. AFAIK, ANY stereo amp, tubed or SS, that doesn't prohibit combining the common terminals can do this.

Bridging involves driving the 2 channels with opposite-polarity signals and using only the positive terminals for driving the speaker. The result is FOUR times the power because the powersupply Voltage is combined (doubled), and that quadruples the output power. HOWEVER, each channel is now driving HALF the apparent load, so many stereo amps do not have the current capacity to quadruple rated power. Only if an amp can double each channel's power into half the load will it quadruple total power. IOW, if a SS amp that's rated at 100WPC into 8 Ohms can deliver 200WPC into 4 Ohms, it's capable of delivering 400 Watts into 8 Ohms.

So bridging is NOT a good idea for driving power-hungry, low-impedance speakers such as Maggies or, even worse, Apogees, but would work well driving 8-Ohm (or higher) systems.

Dan, if the poweramp available to you is indeed identical to the PA section of your integrated amp, buying one and paralleling their channels might be an economical way to buy more power. But you might find a, say, 200WPC amp, used, for as little money. Look around; you're in the right place at AudiogoN.

* Seems I've written this a half-dozen times already.
** This can NOT be done with amps such as the Spectral DMA-100 that prohibit the joining of the negative terminals.
Bridging is one thing, but paralleling is another.

You certainly won't get an increase in power by paralleling since the voltage applied to the load will be the same (assuming each output stage has infinite internal impedance), and power is voltage squared divided by load impedance. Bridging works because it effectively places the two channels in series (an oversimplification, I know)and doubles the voltage across the load (which in theory yields 4X the power).

Real amplifiers don't have infinite internal impedance.

If you parallel the two channels as Jeffreybehr suggests, then the load impedance that each channel sees is the speaker impedance in parallel with the impedance of the output stage of the other channel.

Most transistor amps have very low output impedances (inversly proportional to the damping factor), usually well below 1 ohm. Thus the load each channel sees will also be below 1 ohm, since the effective parallel impedance will be less than the smaller of the two loads in parallel (the other channel and the speaker).

Most amps will activate protection circuitry, blow fuses, or worst case smoke in this scenario.

It's just basic Ohms law.
Nad integrated amps used to be able to run as a mono amp.I used a 7100 receiver in mono for a centre channel amp to match the greater power of a couple of nad 2100 power amps in a home Theatre.
If I were you I would look for a better power amp and forget what the dealer said because unless you can run the integrated in true mono you will not get double power out of just one channel.I would take my business elsewhere if told this from a dealer.
Ghost, I know you're wrong but I don't know enough about it to argue your psuedo-science. Paralleling works. SOMETIMES bridging works, as in now having enough power whereas one didn't before.
It's not psuedo-science - it's electrical engineering.

Hook up the two channels of an amp with a common ground in parallel and watch what happens - Hope you don't need the amp afterwards.