for best sound its better to only have front speakers and subs. you can do some mid bass speakers in the back doors to add depth but can be hard to get the sound stage right.
i wouldnt suggest putting them in that peice. they wont sound bad but that piece does move around a lot, if you have some higher powered subs it could damage them and the sound stage will be pulled to the back a good amount.
hn155: Rockford punch pro speakers, t400.4 deh 80prs, full audio build to come. working towards 175hp n/a, simple but fun.