Stereo removal:
http://carstereohelp.com/strinfiniti.htm
I suggest Nakamichi if you can find one (ebay), because they sound absolutely outstanding and look very clean and neat without any idiotic looking dancing lights. Otherwise Pioneer, Clarion, and Alpine are high quality. My dad just spent $400 on an Alpine for his MB, and they sound as good as ever and look tasteful compared to years past.
You'll end up either wiring it into the Bose amps or bypassing them altogether, with new wires going to aftermarket speakers.
If your Bose amps are still in good shape, consider a CD head unit from a later Nissan, like a Pathfinder or something. A $18 adapter allows you to use 95+ Nissan/Infiniti head units.