The mixer interface is basically a dj board for a computer software, not really karaoke friendly.

That sound interface may work fine to plug the mics into, again I am not very familiar with connecting mics to a unit like that, I prefer using the USB interface to plug into an external mixer along with the mics in the external mixer - then plug the mixer into the external PA. It may work fine. What are you using for the PA?

The mics are fine for basic entry level home use. Probably will have a little more handling noise and maybe a little on the tinny side - where a regular mixer could help more as you can eq the mics individually.

Unless you are planning on making recordings, I think you may possibly be looking at things backwords.

You can send the output from your PC INTO a mixer, where it can be mixed WITH the Microphones, and the entire output sent OUT to an amp and then to speakers.

An external soundcard can give you a more direct, noise-free path to the mixer.

Of course some soundcards are meant for home recording, and have inputs as well.

Here is my advice, but I may be shot down by other professionals on here - My advice is strictly intended to serve your needs for home and casual home parties - not pro use.

For a non-professional home system, I use a Fender Passport Pro PD-150. It is extremely portable (like a large suitcase - and under 40 lbs.), packs 75 watts per channel, a built-in mixer with reverb, 3 mic inputs as well as a stereo input and effedts return.

It sounds excellent and clear, although lacks some bass response. It has excellent feedback elimination, and the speakers can be mounted on standard speaker poles if you like.

It runs about $500 - $600 depending on the deal (zzounds.com is usually the best). Usually they throw in a basic microphone and cord as well (something to get your started).

All you would need is your laptop and karaoke software to run through this. You would simply use a converter cable to convert your headphone out on your laptop into a dual RCA jack to plug into the stereo input on this mixer.

Of course you could still go with an external sound card if you like.

I have this exact system that I have used for several years at home and at friends houses and it has never ceased to amaze people.

For home use it should be just fine. It will be better than the home stereo for sure as far as karaoke goes.
If you have a chance you may want to find a local store that has one of those in stock. I personally do not care for the sound, the mixer is extremely basic with simple high/low eq on the mic channels - most vocal adjustments are going to involve a midrange, but you can fake that adjustment with the high/low, basic reverb only (no digital multi-effects) & a basic 'tone' control - one knob that adds highs in one direction & lows in the other on the main & no room to upgrade - ie can't use an external mixer with it. Musicians Friend has a pretty good return policy though if you find it not what you are expecting.

Thanks for pointing that out. I didn't know what kind of adjustment the built in mixer has.

So I'm going with a dedicated mixer. What would you recommend for speakers for home use?

PA speakers or studio monitors? A friend of mine suggest 2 KRK Rokit 8's.