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It's tough. I had to get at mine from behind.

Tried this?

Man that guy in the vid made it look so easy. Ok, I used 3 nails each side to remove mine. What I did was remove enough trim to be able to get my hand around the back and then feel the clips on the side. If you can imagine it, I had my hand stretched behind the unit feeling the clips while putting the nails through the holes in the front making sure they sat properly. Others have gotten them out easy but mine didn't want to budge. Still incredibly painful but it came out. If you are still stuck tomorrow I can take a picture.

Download the "entertainment system.pdf" file on this link and start at Page 33 of 74: https://drive.google.com/folderview?id=0B3YbfB30DxW0bEdwS0xSNGVXMzA&usp=sharing

Basically there are two long thin plastic horizontal snap-in tabs on the side of the stereo unit.
Use a small screwdriver or credit card to pry them off.
Behind that you will see there are a few of holes.
The guide talks about a SST Removal tool - I just cut up a metal coathanger and made mine (similar to Figure 38).
Insert the U-shaped metal "tools" into those holes as far as they will go (no need to use force) and pull backwards and outwards simultaneously - this pushes in the retaining tabs and the unit "should" slide out - in practice it takes most guys a while to get it out. The stronger your "tool" and more "snug fitting" in the hole is, the easier it will be - my coathanger "tool" probably wasn't strong enough which is why it took me a while.

You could read this thread
http://mx5cartalk.com/forum/viewtopic.php?f=78&t=28063
Titled "The Idiots guide to replacing a stereo in the NB8B"