2005 Ford Explorer XLT
Single CD, AM/FM with sub

I am having a problem with the factory head unit where it won't eject a
CD, so I am starting to research the options I have to replace the
factory head unit with a "real stereo".

Since I have a limited budget and really can only afford a new H/U now,
my main question is whether or not I will be able to utilize the
factory sub (and the amp that drives it; I presume it has it's own amp
anyway) or not with an aftermarket head unit? For example, is there an
aftermarket harness available that will supply an aftermarket h/u's
line level signal to the factory amp that drives the sub? Or will I
lose it's capability and be forced to replace the amp/sub or else just
forget about a sub altogether until I can afford it?

I realize that the OEM amp/sub are not all that great but I also think
that using them is better than not having a sub at all and just using
the door speakers.  One has to live within his budget unfortunately.

On a related note, does anyone know the specifics of this audio system
in the 2005 XLT? Does the head unit supply all power to the door
speakers? Does the sub have it's own amp?

Thanks in advance!

Bob