I replaced the Clarion Cassette Receiver w/Graphic Equalizer that was in my
'91 9000T.  No problems at all.  I bought a Blaupunkt head unit from
Crutchfield, and they even included an adapter that allowed me to plug
directly into the car's existing wiring harness.  I think the amplifier
(that your local retailer mentioned as needing to be bypassed) is only a
part of the Harmon-Kardon systems in the newer Saabs.  The amplifier in my
Clarion was part of the radio cage and came out (somewhat) easily as I
removed all the old radio components.  The anti-theft feature is wholly
internal to the radio and only comes into play if power is restored to that
radio.  Since it isn't part of the car, the factory radio's anti-theft
feature can't interfere with an aftermaket replacement.

If you have replaced car radios before, this replacement should be no
problem for you.  The greatest difficulty you may have is deciding how to
fill the second DIN slot.  At the time I did the work, Blaupunkt offered an
in-dash CD changer to help me solve that problem.

I hope I answered all your questions.  Let me know if you have any others.

Walt Kienzle
wkienzle (at) sbcglobal.net