Hey fellas how youz going?

I just have quick question about my 2005 C180k's audio.. i have to much bass and not enough treble. i have a Classic and i want to put 2 splits where the rear headrests are. classic does not have any speakers there so its just empty sockets and i was wondering if i could put splits in there?
I went down to the audio place and they told me theyd have to cut the back steel from the boot out to get into there to install the speakers and that would weaken the car structure n so on.. . but i looked at it myself and im not sure if they know what they are talking about.. you guys probably know more than those guys so asking for your input. cheers boys.