Whoops I didn't mean to post anything, sorry folks.

Not going to get into the debate about FDs and APs, but it is worth noting for those who might encounter same issue this in the future-

If you have a Stab/Mach trim failure that won't reengage, push and hold the red AP Disconnect Button for 20-30 seconds, then try to reconnect the trim. In my own personal experience (both in the CRJ and the Citation), this simple act will clear 99% of the issues that aren't related to "EFIS COMP MON" type things. (Think of it like a "CTL-ALT-DEL" for the trim system). Don't know why they don't include this procedure in the QRH...

Sounds like you guys did a good job though!