getting ready to buy a boss loop station rd 2 and I'm not quite sure if I can use it with my pa system. have a Yamaha passport pro 400 and don't want to ruin my system. really hoping I can do this.
If anything, you may run into the issue that the loop system is too quiet coming into your mixer, and has trouble getting loud enough. If that is the case, you should consider purchasing a tool called a DI box, that converts your 1/4 inch guitar cable into an XLR cable like a microphone (it does other things as well but that is the most obvious). This will help deliver a signal that can be usable in the PA mixer. The signal chain will then be:
Guitar > Loop pedal > DI box > mixer
When you first connect the guitar to the mixer channel, turn the mixer channel volume all the way down. Set the levels of anything else you are using like a microphone or drum machine that you are more comfortable with, and then slowly bring up the guitar channel until it is balanced. This will prevent any loud popping or unexpected feedback.