A soundcard is a must. But do you mean do you need to replace the factory soundcard? It is not a "must" that it be replaced but, your factory soundcard will be a bottle neck of your signal chain. All the nice mics and pres in the world wont matter if you are using an onboard soundcard. You might as well be using a PC mic. I feel safe saying that a cheap mic and a good soundcard would sound better than an onboard soundcard and a $5000 mic.