As far as a sound card goes, it depends on what you consider a professional
card. At this point, personally I tend toward the USB external cards
myself, partially because there is only one USB audio driver for all sound
cards. So if you have a high-end USB card, there's a really good chance it
will work with no problems.
I personally have a Creative Xfi USB and am quite happy with both the sound
quality and signal strength; it puts out a good loud signal. But it is only
a 2.1 channel card, and while it would probably be fine for playout, isn't
exactly good for studio production.
We've also had very good experience with SoundBlaster Live cards.