Cassette HU

I'm pretty sure its not the Speakers because these speakers aren't sh*tty.  They are Infinity 5002i at about $50 a pair.  And also, the JVC head unit, flickers like crazy when I push the volume up. 

Your right, someone else told me to check this as well, so I'm going to go out tommorow and check that out.  Thanx.

I think the Fit guide specifies the rear quarter panel in which there is a cut out for a subwoofer.  And that spot might handle that big of a speaker, cuz from what I recall, the fronts are 4 inch speakers and the rears were 5 inch speakers, and fitting these 5.25's was a pain as it is.  So I know anything bigger would not be possible.  The subwoofer compartment towards the lift gate however seems to have a cut out for a 6x9 and that is where I want to add a small sub if the change in Head Unit doesn't make things better. 

first and foremost, yes indeed check phase of your speakers... sweep the balance control all the way to one side... how does it sound? sweep it all the way to the other side, how does it sound? now put it back in the middle... how does it sound?  if it sounds like you are listening to it in a wind tunnel in the middle position you have a speaker out of phase...

if however, they are in phase you may want to consider that forbidden/Rob had a valid point.... how did the OEM speakers sound with the JVC HU?   good?    then why blame the HU?

many people when replacing speakers dont take into account the different efficiencies of the speakers... a factory (OEM) speaker as a rule tends to be very efficient whereas aftermarket speakers ( especially better quality ones ) tend not to be..... it sounds like you simply need more oomph to now power these Infinitys vs. your OEM speakers and now you are finding that the JVC doesnt have that oomph.... it's not a fault of the HU per se..... many people going from cheaper, efficient OEM speakers to an upgraded speaker find that deck power suddenly doesnt do it anymore..... which is why a simple upgrade often snowballs into adding an amp, then a battery, then an alternator to charge the battery, etc, etc.....

if your Infinity speakers need a little more power to make them shine i dont see what swapping head units will do unless you plan on adding a power amp to that new head unit....... regardless of brand i doubt if you'll be happy simply running deck power....