Hello! My name is ***** ***** it is my pleasure to assist you today.
Harmon Kardon no longer officially supports these speakers on Mac, so support on newer versions of OS X is very hit-or-miss. You mentioned that, in the past, you've been able to get OS X to detect the speakers by unplugging them/plugging them back in. That being so, here's a question: have you tried additionally disconnecting the speakers from power, then plugging power back in, and *then* plugging them back into the computer? In some instances, performing the tasks in exactly that order allows the speakers to be properly re-detected by OS X.
Please let me know whether that works (or if it was something you already tried) and we'll look into this further, if needed.
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