JR - This may sound too simplistic, but you require interconnects which adapts to fit your connectors. If the mixer only has "red and white phono outputs", the signal is unbalanced from that point on (as opposed to being a balanced output which is the usual case when an XLR plug is utilized). You simply need to either buy interconnects which move the unbalanced signal along from phono out to XLR in, with the correct (XLR) pin wired as hot. Then a set of cables for the speakers which go from speakon to XLR, with the correct pin wiring. If you cannot find pre assembled cables to accomplish this task, you can use adaptors at the appropriate ends. Adaptors allow more contact points that could give problems in the future. The best solution is to plan out and put together a system where all the connections agree. As you update the system, that should be a priority.