I think its a combo of your deck sending out a distorted signal and also your speakers hitting thier limit. A crossover will help with this but it will be hard to implement without an amp on the highs. I would get an amp on the highs to help them keep with will all the bass and you can use its crossover to cut out some of the bass so they wont bottom out. Are you interor speakers stock?

As far as your subs its probably that the kickers may be a bit more efficient and this makes up for the power difference or it could be his am is jsut really putting out more than yours. It could also be a function of the box ie size type ect. Usallly bridging an amp that is say 150 x 2 will be 300 x 1 channel usally same total power but distributed different. Some amps will put out more bridged but a lot depends on the ohm load. Most people bridge sub amps. You should do this if your subs are in a box like a bandpass box or where the subs share the same air space.