If you see the M on the UFC on one radio or the other, it just means Manual.
HOWEVER:
You can punch frequencies in directly to the radios. Select the radio you want (1 or 2) then punch the freq into the UFC. Say, for example, you want to have the Com1 to be 121.90, and the ILS (NAV 1) to be 109.50. You don't need to have the M selected for a radio. Just make sure that
GRCV
SQCH
CPHR
AM
MENU
Is showing on the right side of the UFC, If it's not, just deselect whatever you had chosen on the keys on the bottom of the UFC. If you hit the TCN key, just hit it again, and voila! Do that for whatever key you had activated. Then type in whatever freq you want on the keypad. In this example, punch 1-2-1-9-0 and hit the ENTER key. Done.
To set NAV1, select the TCN or ILS button at the bottom of hte UFC, and punch in, in this example, 1-0-9-5-0, ENTER. Done.
It's not hard to figure out. Just do it a few times, and you will have it locked in, no pun intended
You can see you can enter whatever freq you want, in whichever radio you want. There aren't any "limitations", other than the proper frequency band for a particular radio. For example, if you try to enter a COM freq into a NAV radio, you will get an ERROR displayed.
Does that answer your question adequately?
Pat☺