Any bridged amplifier "sees" an effective load that is half the load seen by a single channel, and the amplifier's output impedance is doubled (damping factor is halved). Most amplifiers are rated to twice the minimum load impedance when operated in bridged mode. And a number of mono amplifiers are also bridged designs. For that you get theoretically four times the output power (most spec less than that, often closer to a doubling, due to other factors at play like thermal management -- heat sinking -- and power supply capacity). You also gain some additional distortion cancellation and a little more noise. Note the output terminals "float" in a bridged design so be sure not to short any output connection to ground (this is more a problem on the test bench than in the real world). All of this is true for any bridged amplifier, stereo or mono. It is not a "gremlin" or likely to cause problems unless you have very hard-to-drive speakers dipping very low in impedance.
I know of several folk driving Revel Salon2 and other relatively hard-to-drive speakers using bridged AHB2s so I expect they will do fine driving your Yamaha speakers. You might want to check an online calculator (e.g.
http://myhometheater.homestead.com/splcalculator.html) or measure to see if you really need that much power, however. I would start with one AHB2 and see if its (sophisticated) clipping indicators ever flash then invest in a second later if you really need it.
FWIWFM, HTH, IME, IMO, YMMV, my 0.000001 cent (microcent), etc. - Don
