If they're "pretty high end" and they told you they can't keep their serial numbers sequential without duplication, I'd have a hard time believing they'd support or warranty their products if something happened. Major red flag for the brand.
Duplicate Serial Numbers
As I was browsing A'Gon, I came across a pair of speakers for sale with the same serial numbers as mine, which I bought from the manufacturer directly. In my experience, serial numbers typically are unique. So, might this be a mistake or could the ones for sale be fakes? I've already written to the manufacturer (have yet to hear back), but was curious as to your opinions. Thanks.