No problem with the audio.Sometimes the engine sound will cut out. but that a known glitch that happens to everyone running the game on todays faster computers. AOD with Dos-Box sounds smoother than Caod on my machine.I've never run the game with an external sound card so I can't comment on that one.It's the first time I've heard about that problem. Maybe something here:
http://www.subsim.com/tips/tipaod.php will help.Good luck.