Hardware setup

So I'm pretty new to internet broadcasting, and I'm having trouble with choosing the hardware. I have a small mixer, laptop, mic and an encoder (currently using Mixxx) I'm doing mostly talk radio so i don't need anything too crazy. However, I want to play sound effects, some royalty free music occasionally, and commercials as well as station IDs and some promotional stuff.

I am 99% certain the issue is my computer's sound card, but I'm having trouble with getting the mix out to my stream without either an echo, or having the feed repeat on me every few seconds, consistently getting lower as it goes. If i decide to go blind with the outtakes, it's fine but that is disastrous from a sound and timing standpoint.

What are others using? Should i be investing in an external sound card? A microphone processor?

Any input would be greatly appreciated .