Thank you guys for these answers.
I maybe found in the user manual an explanation of why it is not possible:
"The HX Effects device signal path is stereo, carrying two channels of audio. When the device is fed a stereo input source (i.e. - when discrete left & right signals are connected into the device's Left and Right input jacks), the source audio is processed discretely in stereo, wherever stereo blocks are used within the path. Whenever a mono block is added within a path, both channels of audio are combined and sent out of the block as mono."
It looks like some of you think it would work, can you try it?
Maybe I need to buy one and just return it if it doesn't work...