I've dealt with them on many occasions with car audio and home audio.
These guys know what's up, and are ALWAYS willing to help. If you just have a simple question, or if you are looking to get a great deal on a system, these guys will hook you up right.
Jim is my guy, but they all know audio.
They deal Rockford, Kicker, Alpine, Pioneer, and Sony for car audio. (I may have missed some)
They do custom set-ups, simple installs, and fully back EVERYTHING they do. I even got a replacement sub from them after having them tune my amp and blowing my sub later that day. They seriously stand behind their work! I doubt you'll find a better shop in SD.