You have a TON of options regarding what head unit to use. As far as removing the screws, you'll need an impact driver. If you don't have one already, you can pick one up at your local hardware store for around $10 or $15. Works like a charm. If you try to remove the screws without it, you're almost assured to strip them.Now, on to the fun stuff! Depending on what year J you have, there are two different adapters you'll need to install an aftermarket unit using the Bose speakers.
Here's a link for a 1993 J30 adapter:
http://www.crutchfield.com/S-6...4NN02
Here's a link to the 94-97 J30 adapter:
http://www.crutchfield.com/S-6...4NN03
They both cost $39.99 through Crutchfield. Others have bought different brands, but this is the only one I've used and it works great.
You need to decide whether you want a single or double din head unit. I originally had a single-din Sony Xplod unit in my car. It sounded great, but I ended up switching to a Jensen double din DVD head unit and love it. I prefer utilizing all the space left from the factory unit instead of having the storage sleeve under the single din.
If you've never done this before, I recommend you make your purchase on
http://www.crutchfield.com. Most, if not all units come with free installation kits and instructions, which includes the storage pocket should you decide on a single din unit. The Sony was my first one done on the J and it made all the difference in the world. Only took 40 minutes to do. From time to time they'll offer free shipping on their orders and their prices are competitive.
Even if you don't buy from them, they have a filter that you can use that will only show what will fit in your car. When you do this, don't input the J30 info, because it will tell you no information is available. Use a Nissan Maxima WITH THE BOSE SYSTEM and whatever year J you have. Example: if you have a 1995 Infiniti J30, input 1995 Nissan Maxima WITH BOSE SYSTEM to get the results you need, The sizes are identical. You'll then be able to see most of what's on the market and shop by price or features. Remember, you get a free installation kit and instructions with this.
Most people who go with aftermarket head units say the Alpine units fit best. Kenwood units will stick out (my Sony did a little, too, but the Jensen is pretty good).
Another tip: when you do the installation, don't screw the head unit in until after you have tested to make sure it works, and to calibrate the levels on the adapter. You may have to tinker with the levels or even change a fuse in the back of the head unit (if it has one) and it will only piss you off if you've already put everything back in place before you find out.
Here's a link that give you step-by-step instructions on how to remove the head unit. It used to be free, but they charge a nominal fee now. Someone else may have the instructions somewhere for free.
http://www.carstereoremoval.co...P.htm
Here's another link that may help from http://www.fuzzycats.com:http://www.fuzzycats.com/docs/bose_replacement.pdf
I hope this helps! Feel free to ask any other questions you may have.