External Microphone Issues

Hi fellow Deluge lovers,

I just invested in this fancy little machine and love it. However, some things are giving me a headache, mainly the external mic setup as I want to use the Deluge a lot for looping vocals.

I have a classic SM58 and got myself an iRig pre 2 to be able to plug it into the Deluge's mic port. But strangely, it barely works. It is only super super quiet when I record, barely noticable. I already set the gain to high and also maxxed out the gain on the iRig, which didn't make it much better and only made the background noise worse, like a loud humming.

What am I missing? What can be the issue here? is this sort of setup simply not working?

Thanks for any help!