However, since you are already using balanced line interconnects to the power amps, why don't you move each monoblock power amp to be adjacent to the speaker? That way you can reduce the length of the speaker cable to be much less than a metre (maybe as short as 6"). That is what I have done.
Yes, I did think about that at the time but decided against that approach as I would have had to increase the length of the interconnects. The power amps sitting in the middle of the speakers seems a nice balance to me. There are no children in the house so it works ok for us. I can see the benefit of that approach though.