You can improve the sound of ANY system by getting better speakers.
Home theater speakers are a terrible choice for live voice. Most have less impeadance, (resistance in ohms), than what the mfr. rates them at. Look at speaker ratings in the Consumers Guide Buying Guide and you will see what I mean.
I would recommend that you get proaudio speakers with 15" drivers for bass. Spend all that you can afford.
Using a home reciever in place of a professional power amp is also a poor choice. You need an amp with a high slew rate. This is the speed that the amp responds to input. You also need plenty of dampening power. This is what makes the speaker cone stop when a bass note stops playing. When you turn an amp up the total harmonic distortion, (THD), goes up. Get an amp with more power than what you will need. When an amp fails to make a compleat wave form, it clips off the top of the wave which sends DC to your speakers. This is known as amp clipping, and is not a good thing.
The majority of home recievers are rated down to 6ohms, while pro amps are all rated down to at least 4ohms, and many go down to 2ohms.
If you connect 4, 8ohm speakers to your system, 2 per side, you will be running at 4ohms, (or less if any of your speakers have less than 8ohms of resistance.
Most, but not all power amps don't have any tone controls so you should get a small mixer. A mixer will have better preamps for the mic inputs than what you will find on karaoke players. I like the features found on the Alesis 6 channel mixer found at musicciansfriend.com shearch for product #630157. This is an EFX mixer that has echo, chorus, reverb, etc. built in. A mixer will allow you to use a mic cord with an XLR connector as opposed to one with a 1/4" connector.
You can also go with a package(d), PA system.
They start for about $200 but remember, you get what you pay for.
Check out
www.carvin.com and
www.musicansfriend.com
Poor mics are a drag expect to spend about $50, but don't go over $100.
Shure SM57s and SM58s are a solid choice for around $100, but you have many mics to choose from. You will find a wide range of mics at the stores listed on Karaoke Scene's homepage.
The bottom line is:
1st get the best speakers that you can afford.
2nd get a pro audio amp.
3rd find a mixer.
4th poor mics are a drag, expect to spend a least $50.
5th use mic cords with XLR connectors and heavy gauge speaker wire.
You don't have to fill this bill in any particular order, but, get the best speakers you can afford!
I cannot stress this enough.
GET GOOD SPEAKERS!
Kojak