The MR1200PA was designed with a built-in PA system, so you can use your wake tower speakers or other stereo speakers to make announcements. When you key the microphone the audio source is muted and your voice comes out over the speakers.
Great product from it's adjust-ability for number of speakers/channels and types of connections for each speaker, to it's overall function. Built in PA is an awesome feature for making announcements, although it could be louder in my opinion. LPF and HPF built in are great. The only issue I've had with this product is overheating, though it should be noted: I have the amplifier located in an area with minimal, almost no air flow. I added some fans to the area to circulate air and haven't had an issue since. GREAT product overall, I would buy it again.