I can't get a mic to work in the mic/line in port. I can select it in system preferences, but it doesn't detect any sound. I search the forums and apparently the older macbook pros had a combo input in/out, or the line in only accepted powered input (ie not headphones). However, on the 6,2 (June 2010) macbook pro 15" I thought the line in was a typical mic jack that would accept mic input. Is this not the case?