it is 61/2 but the way that mitsu made them makes it impossible without adapters to space out the speaker to install aftermarket speakers. so yeah you will need them kinda sucks but one of those things u need to buy if you want your speakers in their.

 

your gonna need adapters.

on my 08 lancer i took the stock speakers and "ripped them out" and i modded the housing of the stock speaker to fit the new blaupunkt 6.5" i bought. This worked well and the speakers just sat in place like they were OEM. By modded I mean I had to drill holes into the stock speaker housing and use nuts and bolts to bolt the new speakers down to the housing.

I wish I had pictures of this but I gave my 08 lancer to my dad and I bought an 09 GTS!

oh and if you dont want to tap into the rear you can add a sub by tapping into the rear speakers

I did this and it worked just fine. But i would just put an aftermarket hu because the stock sucks

 

Or you can stick with you stock sterio and buy a "factory sound processor". Don't have one yet, but I here the JL Audio CleanSweep processor work great.