I just put together a 4U rack system for stereo sound on the go. It has a Crown XLS 202D Amp, a Behringer Feedback Destroyer Pro, and a Behringer MMX882 mixer.
The only thing that's missing to make it into a great karaoke system is effects on the mixer to add some depth to the singers voices.
Tim, the MX882 is designed for line-level audio signals. It has no microphone inputs. What are you using for mic preamps?
The Ultralink doesn't offer any aux sends to send the vocals to a reverb unit. Would you run the whole mix through the effects? I wouldn't.
Actually, the MX882 has the equivalent of a send on each channel. In MIX mode the channel input (dry/unprocessed signal) is routed both to the channel output and to the main mix bus. The channel output can feed an effects unit. The wet/processed signal of the effects unit would come back into the MX882 on the main inputs. This can be stereo if your effects unit has stereo output. The ratio of wet-to-dry signal can be controlled by the main input level pot.