You need a "Low Profile" type card for the "S" model (a major reason not to buy the compact case model PC's - they are very limited in add on cards and the power supply is not a standard ATX and although there is an after marked power supply it's still a low wattage model.
I do alot of support on the Dell users forum and always try to discourage it if asked about buying a compact case model.
I do recording (Sonar) on my PC. With a situation like this, for recording I would use a USB connected recording interface unit, if that is what you are referring to "pro audio" for.
If it's just you want a better sound card, do a google search for "low profile sound card". You may or may not find anything.
If you recently purchased this direct from Dell, you have 21 days from the date on the Invoice (usually the day it was shipped) to decide if you want the PC or not. If you don't you must call Dell within the 21 days to request a return.