Lose connection with more (7) arduino's at the same time

Dear fellow Max MSP-ers,

We are working on a project where we use arduino's to measure the distance that is travelled by items that hang on pulleys. We have six pulleys. Each pulley has an arduino attached to it.

We also have one arduino that controls leds based on the input it receives from the other six arduino's.

Every arduino is connected to a hub that has its own power supply and there is only one cable to the Mac Mini that is running the software. (Connecting each arduino separately to the computer did not solve the problem)

We use Max MSP 6 on Mac OS X 10.8 for communication between the arduino's.

Our problem: When we connect all seven arduino's at once we keep losing connections. Everything works fine if we only connect two pulleys and the light arduino, but when we connect more pulleys it keeps losing one or more arduino's.
If we force the Max MSP to always find the serial port again when it looses a connection, then the program crashes or the computer restarts, which is quite unfortunate because we have t climb a 3m ladder to turn it back on.

We have searched this forum for an answer and have found people with a similar problem, but no solutions. We came upon these topics: 1, 2, 3 and 4 .

Somewhere in there we also use Live because we play sounds with Ableton that are also dependant on the movement of the pulleys. So we have three components in our installation: pulleys (= movement), light and sound. Basically nothing works if we do not have a constant stream of data about the movement of the pulleys from the six arduino's. The whole project is quite big so posting all the code would be too much.

A solution would be to connect the sensors in all the pulleys to a single arduino. However, we prefer this setup because it is neater with less wires.

So .. our question(s) is(are): Has anyone experienced losing serial port connection while trying to communicate with multiple arduino's? Is there anyone that knows another solution? Should it not be possible to communicate with seven arduino's without problems or is this asking to much?

Thanks!