Very few decks have low crossover signal that you can use that has the +- feeds you need for the sub.
I replaced my subwoofer speaker in my factory enclosure with a JL unit. I dont remember what oms anymore. My aftermaket deck has RCA low outputs that are preamp, then a small amp powers the sub.
I saw that CFLD deal - should be nice...photos, please, if you have the time, thanks.