By passing the Pre-Amp on an Ashdown ABM 600 ...... How??

[Pirellithecat]

Probably an obvious answer to this, but I've tried and failed so far!  
I want to try my Laney Digbeth pre-amp pedal direct into the power amp stage of the Ashdown.    So the circuit would go Bass>Digbeth>Ashdown Power Stage.  I can get the Digbeth to work via the Send Return Loop, but this means the bass is plugged into the Ashdown and passes through the Ashdown Pre amp before it arrives at the Digbeth.  
Anyone know how to make this happen? 
Thanks

[Beedster]

Um….