Did you try using google with mp3car (or site:mp3car.com - whatever google's syntax is) followed by keywords? (Forum search engines are notoriously lacking or bad.)
The only reason I would see for splitting bass would be for 2 different woofers each with their own sweet spot, otherwise there is no point. (If higher frequencies, location might be another factor).
The splitting would either be with high-power filters, else at the pre-amplifier stage using 2 amplifiers.