That is a link to a cheap stereo amplifier - it will be able to take an input signal and power 2 speakers (with 25 watts/channel) -- but will not be able to take the mike inputs, or provide you with 5.1...
If you want to go with a cheaper - karaoke only system - then the cheapest complete one...
Looking at the diagram he provided -- with mike cables going into AV receiver -- as you stated in one of your responses -- "that is just wrong."
But it is correct for a PA system - and if the diagram is correct - and all they want is a system for karaoke, then a simple PA system would fit the...
You need to find something that is made for microphones and live music - not a home theater system - something like a PA system -- a cheap one can be had for around 150.00
http://www.musiciansfriend.com/pro-audio/harbinger-ha60-pa-system
"This affordable Harbinger HA60 PA System features a...