HELP! Stereo Installation in a 5k

[Sze Hui]

Hi,
I'm looking at replacing the stock stereo in my '87 5k with a cd deck.  I've been shopping around, and according to Crutchfield's website, installing a new deck requires some sort of adapter.  Apparently, this adapter "matches the output level of most aftermarket receivers to the input levels of a lot of factory amps. It also works in many cars with speakers grounded to the chassis. Using this adapter will eliminate the need to rewire speakers."  Does the 5k really require this adapter?  What does installation involve if I don't buy the adapter?  Or rather, what does installation involve, period? I'm hoping one of you out there has done this before and can help me out.

Thanks in advance.
Sze Hui
'87 5kcsqt
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