What is the ideal cross-over frequence (M22ti to JBL sub)?

Gerhard, 80Hz is generally suggested as the crossover setting, but the lowest crossover available on your 912 is 100Hz, so that's what you should use.

Thanks John! How did you know that I have a 912?? I am stunned ...

JohnK is OMNISCIENT and we should not question the mystery of his ways.

Gerhard, Mike's reply is entirely accurate and in my work I have access to dossiers on all Axiom board members which contain even the most personal details. However, in this instance you might be less stunned if you re-read your first post on "...anemic bass?" in which you mentioned your Pioneer 912K.