Low volume when streaming with Atem mini Pro ISO

We use a Soundcraft Si Performer 3 mixer at our church and we send the audio through one of the matrixes into the Mic 1 input on the Atem mini Pro ISO to stream to Youtube. But the problem is that the signal is weaker than we want.
We have it set to Line level (i think) and that helped, but you still need to turn up the volume on the device you are watching from in order to hear everything good enough. And also, there is alot of background noise. It doesn't seem to be coming from the mixer, because if I listen to the matrix output directly on the board, it sounds fine. And we can't really increase the volume on the matrix as it's basically already at maximum and if we increase the overall volume from the board, it gets to loud in the church instead.
Are we doing something wrong, or is there a way to boost the signal to the Atem and not have it affect the volume in the church?

I'm sorry if I seem dumb, but I don't really know much about this.

Sounds like you are running a balanced XLR feed into the unbalanced stereo mini-jack on the ATEM. We use this converter between an XLR out on our Allen & Heath SQ-5 mixer into the ATEM Mini ISO. No buzz or noise and delivers plenty of level. There will be other boxes that do exactly the same, but I use one of these, so can vouch that it works 100% with the ATEM Mini ISO.

https://www.stage-electrics.co.uk/View/ ... As_l86-1qV

Yes I'll definitely give it a try! Thanks