Suggestion for a sound card.

I really didn't find anywhere else more convenient to ask for this help so came here to ask.
I am a bit confused with what i should be buying since i never thought sound cards to be a big factor, the built-in card made do till now. But now i'm considering of getting a sound card for a few needs.

I basically use my computer for gaming + listening to music, mostly. But recently I have taken interest in Audio Mixing/Mastering. A bit semi-intermediate audio work you might say. I help my friend's productions. I normally have to mix his vocals/instruments, which requires multi-track usage. With the built-in card i've been working for a while but i had to face a few problems which some professionals i know said was because of the sound card. Problems were that if I had too many tracks in the multi-track session the audio would just break up and go haphazard which meant that to finish the task i had to cut up the whole session into different sessions and then finish it. This tends to not give good quality as you may figure. And this also happened if there were too many VSTs working at the same time even with 4-5 tracks. I figured these can't be a processor/RAM related issue because all I use is Adobe Audition and its internal effects and just 1 outside VST. And Adobe Audition has been around for a quite some time and people used it before without any problems then.

I looked through the internet and saw that M-Audio gives the best music production sound card[been advised to get that] but isn't that great for gaming. So unless its a last option I'd prefer something else, since i just need multi-track to work properly without sounds going crazy and I don't record anything on my computer so M-Audio cards seem useless[with all the MIDI ports and such]. So, I was wondering if just any sound card will help me out of this or would getting something specific be better?

Thank you for the help.