I added a new "Apple" 5870, paying more to reduce the hassle factor. However, once it was installed (it works great) I have lost audio. My system no longer sees that I have speakers connected (but they are). System preferences has no audio output options. I get feedback hum from the speakers when I disconnect and reconnect, so they appear to be working fine. I know it has to be something stupid ... any idea what (I did a search and found nothing)?