I worked in the car stereo business for over twenty years as and still come out of retirement every once in a while for cool projects. Here is my take on "subs on bike". Don't waste the time and money, first off yo generate any kind of "bass" or bottom end you need a much larger speaker than a 6 inch sub, at best the 6 inch cone can reproduce a low midrange. I've actually put 10 and 12 speakers in side cars and they never sounded very good because reproducing low end bass in an open environment is very difficult and takes a large amount of clean power, which is tough to generate with a bikes electrical system and a large amount of speaker volume which you are limited on space on a bike. Think of the amount of equipment needed to make a concert hall sound good. It has to do with the sound wave of "bass" needing to reflect to increase because of its length it takes a long distance to complete, we called this the "convertable syndrome" when we would install a high end system in a drop top it would sound good with the top up because the bass wave would reflect in the car but with the top down the wave would be lost and to prove this to the vehicle owner pulling the car into the garage with the top down would magically restore the sound. Go with the power upgrade and R and R the OEM speakers to get a good volume. I have the Hawg Wired 300 watt system and Alpine marine speakers on mine 09 and it gives me great sound and volume. Just some other problems are the limitations of the bike electrical system, and enclosure volume. BTW you have to use enclosure specs from the manufacturer of the speakers, not all enclosures are the same just by speaker size.