Yeah but surely each channel is limited to a certain number of watts...by bi-amping even from the same receiver you are providing the speakers with more power...or am I missing something?
What you're missing is the games that manufacturers and retailers play when quoting power figures.
Look on the back of your amp or check the manual for the power consumption figure. Your Sony eats about 240 Watts from the AC mains in full power mode. In electrical power terms, a Watt is a Watt whether it's on the AC input side of the amp's transformer or on the power output to the speakers. IOW, we can't magic up a whole bunch of extra Watts from nothing. What we get from the transformer, minus some loss due to inefficiency, is all we have to drive the speakers and run all the amplifier features. So let's take our 240 W consumption, and say we lose about 4-5% in heat and vibration within the transformer. That gives us roughly 230 Watts rounded up.
It looks like from review measurements that the 1040 can provide 2x100W in to 8 Ohms, 20Hz-20kHz @ 0.01% THD. That looks about right. it means from the 30 Watts remaining, there's some reserve of power for the speakers and to run the amp's features. Let's say there's a 10% margin per channel, so 220 Watt in total for any speaker combination, and that leaves about 10 Watts to cover running the amp and any heat losses.
The 1040 is a 7ch amp, so if we take 220W and divide by 7 we get 30W per channel. At this point you're saying "What?!? That can't be right, can it?"
What you need to remember is that it doesn't take many Watts to make a lot of noise. Your Boston speakers might be 85dB er Watt per metre. That means all they need is 2-3 Watts a piece to get close to the reference volume level of 85dB that many amps use for speaker level set up.
How come then the 1040 is quoted at 1155 Watts?
The answer is smoke and mirrors.
The AV performance is measured with only one channel driven, and with a 1kHz test tone which draws very little power from the amp compared to 20Hz-20kHz, and at a relatively high distortion figure.
The Wattage figure they get is 165W. In effect, this is the saturation point of the output transistor pair for that channel.
It used to be that manufacturers would multiply the measured power by the number of channels on the amp. Some may even still do this. Most now though leave customers or retailers to jump to that conclusion. Let's face it, 7x 165W sounds a lot more exciting on a spec sheet than 7x 30W.
The bottom line then is there's a 230W cake. It can be divided any way you like, but it'll never be bigger than 230 Watts.