| One big issue is balanced versus unbalanced connections. If part of your chain converts your signal from unbalanced to balanced, and if you use only balanced connections from that point on in the entire rest of your chain, then you can send that signal to the PA. If none of your devices converts from unbalanced to balanced, or if you go back to unbalanced connections later in the chain, then that output is not suitable for sending to the PA.
The reason is noise reduction. Regular instrument cables (which are unbalanced) pick up more noise the longer they are, and if you send an unbalanced signal into an XLR cable it is still unbalanced and will still pick up noise. Balanced connections cancel out any ambient EMF noise that the cable would have picked up.
As far as impedance is concerned, you should not have a problem. Most pedals and rack processors have a low enough output impedance that you will have a good impedance relationship with the PA inputs, and minimal loss over the length of the cable. | 
