5150 + GT Pro help

Hi

I've been trying to use the Boss GT-Pro through the effects loop on a 5150 to add effects and an extra channel. Everything sounds really cool when it's quiet but when you turn it up for the stage, there's a huge compression happening and I haven't been able to use this setup on stage yet.

Any ideas how to fix this problem or is the GT-Pro just not meant to be used this way :confused:

Thanks

you can't have any pre-amp action going on in your loop