make sure its the proper power adapter. If its not it will introduce all sorts of noise. I would use a proper adapter from behringer. Of one of the adapter damaged the internals.
That depends on what you want to end up doing. You will end up patching into/out of the jacks on the front. You do not come out of the jacks on the back to the crossover.
Watch your impedance, when you add speakers the impedance will change. example 8 ohm speaker placed in parallel with another 8 ohm speaker the impedance is 4 ohms, placed in series the it is 16 ohm Me I would place in parallel this mixer should handle 3 ohms
Read the manuals for both the mixer and the active speakers. If you do not have the manuals, download them from the manufacturers websites. If you don't know hw to use equipment, don't buy it.
Hi, the power light should not "blink" at any point. It should always be either on or off when either powered on or off. Sounds as though the internal toroidal transformer has gone faulty (common issue) and requires replacemnet by a professional.