OK it seems that I finally have resolved this. Here the settings i used:
Earforce FX Loop mix set to 75%
PF Output level set to -3dB
Input / Output set to Guitar/Amp
Bypass Mode: Relay
Killdry off
It works more or less perfect. Only on FX like Crystals when reverb / feedback is set to relatively high values it creates some noise when the FX loop is activated, but it's by far not as disturbing as before!
Thanks for your help!
