Not unless it is a 4 ch amp. doubleing up or "bridging" causes you to lower the impedence "ohms" where as you are taking a 4 ohm amp and now running it at 2 ohms. The distortion tends to double but then again so does the power.

You'd be sending the same amount of wattage to the sound bar as you would the subs. Not to mention if you have it set up correctly you have a low pass filter on the subs, vrs full range meaning all you are getting are bass notes out of them....not all the vocals and such wich subs arent usually designed to reproduce. If you bridged each channel and ran the speakers in paralell with a low pass filter you would only be getting the lows out of the sound par and none of that high frequencies.