Not like they don’t make 6v led lights. If you don’t want to complicate things with even more electronics altering voltages.
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Should work fine but some extra circuitry that can cause problems in the future. LEDs run on about 3 volts and are wired in series to get to 12 volts. The step up deal converts DC to AC to run through a transformer then rectifies that back to DC for the output. I'd go with the six volt option but since you've already bought the units you'll be fine as long as the current ratings match up.