I checked the website, there's no documentation that I can find.
http://www.bubblesound-instruments.com/MIX6.html

You may want to contact the manufacturer. There are mixers that are intentionally made with low headroom so that distortion can be used as an effect. I don't think this one does. I'd ask the manufacturer how many volts it can take at unity gain before distortion. In most mixers, you can intentionally overdrive the sound by starting with an already loud signal and making it louder.

I don't think you'd have an issue unless your drums are already slamming the inputs.
-- Ronin1973

Thanks Ronin for the tip I'm new in this fantastic modular world