Beep,
I was thought just the opposite would be. I was thinking of the two what I will call the default Pro Channel compressors, as well as the quad curve EQ, that only one per channel strip can be used.
But the exception to this would be if you bought any of the non included compressors, like the PC4K-S, or the CA2A, that those could be used together with the standard compressors. Maybe more will chine in on this.