He misses a major issue which is the outputs. Cheaper DJ mixers have unbalanced RCA outputs. However, even cheap mic mixers typically have balanced XLR outputs. You will always want to do your long runs to the powered speakers with balanced lines. The other thing is the input and output levels. RCA connections are normally designed for devices with a -10 dBv line level (0.316 volts). XLR connections are usual for +4 dBu line level (1.23 volts). If you run the mic mixer into the controller, you may inadvertently clip the AUX input even though you are nowhere close to full scale on the mic mixer.