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.
