Insert an FXL (Not Send and Return blocks) in your signal path (Grid)
Connect OUTPUT 2 to the input of your preamp
Connect Output (line Level) from your Preamp to INPUT 2
That should work. Please loom at page 67 of the AxeFX II manual. You will need to have your FXL block near your normal input and before your selected amp.
As far as impedance is concerned, it's unlikely to have any impact - neither the output or input on either device are high impedance. High impedance to low impedance creates a problem because the high impedance device is not driven correctly.
Try this and see how it works.
So i can't have the insert preamp as last block at the grid before output the signal? :-/
Alright,do you think its a bad idea in general actually because of the Axe poweramp, cab sim. or so?
All depends on what you want your preamp to do. There's little benefit having the FXL block just before the output unless you want the AxeFx to add some further EQ after your preamp. Unless this is the case, just route your output 1 direct to your preamp and then to your power amp.
Generally preamp go at the beginning of your signal path to add tube warmth to your sound. If that's what you want, just use AMP block and select Tube Preamp and don't bother with your external preamp. Try this before you go and spend money on a preamp.
What is your setup? What comes after the AxeFx?