when you are running the amps in bridged mode, you are increasing the maximum power output of the amplification circuitry, but you are effectively halving its current handling capability - per watt.
When you try and draw more current out of an amplifier than it is capable of providing the voltage output to the speakers will drop. Being as peak power is consumed when your signal is at a high peak or a low trough this will manifest itself as horrible distortion in an excessive case but a more reasonable case you will just start to loose control of your bass cones as they require the most power to move. Your amp might throw the cone forward, then not have enough power to stop it moving forward so much and 'overthrow' the cone. I don't mean overthrow to damage, just to distort your sound. You'd end up with horribly muddy mid/bass if driving your amplifier to its current handling limits.
That said, a speakers impedance is actually a speakers 'nominal impedance at 1000hz' which is precisely it's electrical resistance to a 1Khz signal. However, impedance itself is not a static figure and is highly frequency dependant, particularly in speakers. A few nice graphs of various types of speakers here: http://www.churchsoundcheck.com/imp1.html so you see what I mean. I really wish all manufacturers would provide graphs like this for impedance, response and phase shift btw.
I would be prepared to wager that your manual states not to ever connect smaller than 8 ohms impedance speakers because the manufacturer was wary that they would not sound as good due to the extra current requirements. Thing is this will probably only manifest itself at volumes you're not going to be using anyway.
Bottom line is though, you are NOT going to break your amplifier or speakers by rigging the two together. The very worst that could happen is the amplifier go into thermal shutdown (let it cool off and try again) or blow an easily replaceable fuse... but I give that a 1 in 1000 chance of happening.
Plug it in and have a go, feed something you could call reference music through and try it at different volumes. If the amplifier starts to run out of juice before your ears run out of hearing ability or your speakers start to overdrive then it should be pretty apparant. Sure you could continue to run your amp at those volumes if your ears can take it and if you're happy with listening to a struggling amplifier....
My best guess is that they'll hook up fine and be totally ok for your listening though.