A little late here, but be careful with air solenoids.
If the decoder handles 400 MA TOTAL, then you may have a problem right there... you should measure the steady state current of the air solenoid when activated... (I use 24v air solenoids)
Next they have a very big inductive kick, which can blast solid state switch controllers, you will want to put in a "snubbing" diode across the solenoid to not feed that back into the electronics.
I'm making the assumption that the turnout controller output is solid state, or possibly a reed relay, both of which can be easily destroyed by the BEMF of the solenoid unless protected.
Greg