Audio Systems: Car Audio problem, amp designs, infinity sound

Question
Hello... I have a 2004 Dodge Ram w/ Infinity Sound.  Replaced the head unit with a Pioneer and added 2 12" subs in the back.  Now, the front 6X9s only give out lows.  The back speakers work fine, as do the tweeters but I can't get anything but lows from the front door speakers.  Any ideas?  The folks at Specialist are telling me it was setup this way with the factory amp behind the glovebox and this amp needs to be replaced for $400.  I know I don't know alot about car audio but come on!  Any help you can give would be great, thanks.

Answer
This question is better sent to Ernesto, also on audio systems at allexperts.com so please get a second opinion from him.

Infinity is famous for bi-amp designs.  I am not certain this is so in your vehicle but if it is then it probably needs the amplifier that feeds the high frequencies replaced.  It may very well be the one your service tech mentioned at $400.  But, that is quite a high price to pay.  Probably a generic replacement could to the job at  much, much less $$$.

Also, wiring should be checked to make sure the signal feed is getting to those tweeters in the door speakers.  

Hoping this helps with a good solution.