I have one experience trying to use an MTB front derailleur and MTB triple crank (both LX) with 105 STI road brifters and it didn't work. The cable pull wasn't correct and I couldn't get all three chainrings to ever line up correctly. I wound up using a barend shifter (obviously friction).
At the other end, the 105 STI worked perfectly with the LX rear derailleur.