Audio upgrade advice

[TonyJZX]

I have a crappy Fusion ipod deck running two sets of JBL component 6" splits in the front and back doors

sounds good to me and i don't feel like upgrading to an amp

but...

what can i chuck into the parcel shelf for more bass? i have a big two channel JVC poweramp i can use

what size sub can you get into the shelf?

and is that a good idea anyway since it's just cheap materials anyway (it feels like nothing too solid)

[accentstencil]

They fit 8" subs from factory that fit well. Not sure how big you could go. The 8" subs don't sound bad unless you want super loud bass.