Problem: using Zoom G9 in FX Loop of a high gain amp head

[spycam]

Hello,
today i tried using my Zoom G9 in FX loop of my ENGL SE amp head. It sounded awesome on clean channel with chorus, phaser, delay effects, but when i used high gain channel and wanted to add just some reverb and delay on heavy riffs it sounded very bad. I switched off all effects on Zoom G9, no effects, no tube drives were used at all not even a ZNR or compressor, all was turned off to see if it sounds any better, but the tone was very dull, silent and muddy, like it was only very low EQ frequencies...

Any idea why this happens and what do i do to have the tone unchanged, just delay or so effects added with Zoom G9 in the FX Loop?

Thanks

[T'cat]

i had the same problem with the same unit and boss gt8 using in the loop of my engl fireball.it just coloured the amps tone like u would not believe i tryed everything but to no avail still sucked my amps tone.i seriously dought these units can work in the fx's loop of any tube amp while using the amps gain?sold all that and switched back to good old fashioned stomp boxes wich sound much better sorry i cant help !

[Sixstringhotshot]

That's the drawback to using a cheap effects unit.