After long time of sound testing I would like to share my good experience with this setup: Underwood pup (both elements on) + old Fishman Acoustic Bass preamp/10MOhms Input Impedance/(on max volume,half bass,half treble) running into the Return Input (on GK150MBE) + old first model GK 150MBE. So I am not using the GK internal preamp section at all. By the Master Volume on GK combo ( usually on 9 O´clock is enough) I can control the whole sound (GK line out signal level to the mix console too!). The sound I get is very woody and natural,no scratchy. I think there is a good matching of the input impedance of Fishman Pre with the Return Input of GK. This setup works for me well almost in every situation (jazz trio, big bands).