None of this stuff is designed for Karaoke. The dynamic range of a human voice, uncompressed could easily damage traditional speakers and not to mention that it would drive that Onkyo amplifier into clipping further increasing the chance of speaker damage. It's would be like taking a Ford Mustang off roading. Is it a great car? Yes. Is it the right tool for the job and will it perform well? NO! A Jeep Cherokee would serve you much better.

What you need is a separate system made up of PA gear like they use at weddings and at bars for Karaoke. Think Big horn loaded speakers.