So buy a bigger amp?

I don't need anything lol, I took my setup out of my truck for time being, and the two twelves wouldn't sound good (Sony and a kicker)

Yeah i wouldn't mix subs, and i think imma just upgrade to 12's in my car

If you have two seperate amps and have them set correctly then you can mix subs.

Just have to appropriately calibrate the amp levels so that one isn't going louder than the other, etc.

The subs aren't the same, there for they will always react different and make different notes. No matter how close you get the gains on the amp.

I guess, but you can get them extremely close.

Not comp worthy but you can enjoy it haha

well if you have a two subs, and have one be a 10" and another a 12" then it would probably work abit better

It would sound weird. Both would be hitting at different times due to different subs/amps. May even cause some minor resonance which sounds awkward.

seen a car w/ 2 10' and a 12, didn't have any problems

Maybe you didnt know what to listen for. Same reason kids think Dumbstep has soooooo much eargasm bass!