I couldn't find any picture of custom configurations on these two brothers so, I hope this helps bring some understanding as I had done.

From the back of the F-1X, I am jacked into Full Range from and to my guitar front Line IN port (not shown) If anyone needs clarity, please update this string.

How are you using the F2B?

I will be feeding my keyboad and lead guitar into those ports (channel A and B) respectfuly.  
 
I may also feed each pickup with F-2B for (channel A-2 bridge pickup) and F-1X for (1 input neck pickup).
 
The F-2B functions like (2) peramps in one, which is a solid for handling many configurations. The F-1X is the clean brights and F-2B is for my clean bass bottoms.  
 
Split 1/4 would be used if I decide to test this configuration. There's so much I could do with both preamps

I have to admit that I regret ever selling my F-2B. It was right when tubes became the rage, and I had just picked up a new programmable tube pre, and was offered good money for the Alembic piece.
 
Definitely a good piece to hold onto with many uses!