By the time you add a step-down converter, (16v to 12v) from a cost and complexity point of view you are probably better off just finding an amp that works with the existing system. If you had an existing amp that you absolutely loved (Like an old McIntosh amp) and wanted to incorporate it into the Tesla maybe there's a case for finding a suitable step down converter, but I wouldn't choose the wrong product, then add parts to it to hopefully make it work with the Tesla. There are some very low quality step down converters out there, and to find a quality one in the few hundred-watt range it plus the amp you are trying to make work, you are probably at the same or higher cost than something like the Skar SK-M5001D which is rated to work up to 16v.