Need come clarification - External Audio Interfaces vs Internal cards

I always assumed that a high end internal sound card was all you needed for decent sound along with decent speakers or headphones. However, I have come across a few people who actually prefer an external audio interface linked via firewire. Their arguement is that it shielded away from all the electrical noise that is generated within the case, and it does seem a very plausible explanation. Anyone with an experience with these firewire boxes? The USB ones are apparently quite good, but firewire gets the nod for having better transfer rates, hence why they are generally cheaper.

Opinions anyone?

It all depends on the level of audiophile-ness that you have, and what you are using it for.

First, if you want gaming features like EAX sound processing, you're pretty much going to be using a sound card that supports those. And those sound cards are primarily internal cards.

Second, you want to pick the card with the highest quality DAC. A sound card with a high-quality DAC will be better than a sound card with a low-quality DAC, regardless of internal/external connectivity. But this stops becoming a factor once you get to a certain point. As a general rule, sound cards that cost at least $50 start hitting these diminishing returns.

Third, you want to make sure that your sound output hardware is up to the job. You need speakers or headphones with high sensitivity and detail, to even tell the difference between the electromagnetic interference (EMI) noise. As a general rule of thumb, expect to spend at least $200 on headphones, and $300 on speakers as a minimum in this area. If you bought any of your sound equipment from an electronics retailer like Best Buy, then it isn't high enough quality to make a difference in this area.

Assuming all of those things are equal, then an external sound unit will be better than an internal sound unit, because of the reduced EMI noise. If you really want to take your sound quality to the next level... get an external DAC and an external amplifier (like a headphone amplifier). A sound card will combine the DAC and amplifier into a single unit, which limits the quality of the individual components. Splitting the two components out allows you to combine two best-of-breed products in those areas, and get a very high quality sound setup.