Bridging amps, Good idea or bad idea?

I found this information about bridging amps on the Audio Asylum FAQ. You might find it useful.

Audio Asylum - Biamplification Basics

Bridging (also called monobridging or monoblocking) is the summing of two channels of an amp to give one higher-powered channel. An amp normally rated at 100W might deliver 300W to 400W when bridged. Because of the summing however, the load on the amp is seen as half of its normal value. In other words, an 8-ohm speaker becomes a 4-ohm speaker load, and a 4-ohm speaker becomes a 2-ohm speaker load. Speaker impedance ratings are nominal only. Actual impedance may dip to a much lower value through part of its range. When an amp's current load has been doubled due to bridging, it can often fail to provide the required amount of current into the load. Sonic effects include harshness in the midrange and highs, and thin bass. In almost all situations therefore, biamping with similar amps will result in better sound quality than bridging. Bridging is best left to professional sound-reinforcement applications, where sound quality is secondary.

Good Luck and I hope that helps!

It's true what Kurt's link says. Most amps when bridged cannot drive low impedance loads. Your owner's manual probably states what load you are limited to when bridging.

The damping factor is also cut in half.
More power, (on paper), and less bass.
I've tried it with Adcom & Parasound.
Both brands sounded better using just one channel of each amp.
That allowed the whole stereo amp transformer to supply one channel...
Try it in your setup.

The 840W is rated for 800W bridged into 4 ohms and the sub will help, particularly with an active xover. When you get close to the edge, even the wrong speaker cables can push it over. Depends on the speaker load... resistive, capacitive, impedance...

How about power? That's 2 X 2400W (at ear shattering levels), or 40A @ 120V.

Doubling and quadrupling isn't much of a absolute SPL increase but that's not what it's about. Closer to the point is whether that much power, without the low bass requirement, will benefit your speakers. I could understand for Maggies or Carver A3's.