speaker install back doors

[fotisgr94]

hello everybody i am new member this is my wery first post and i want to ask a questio about my yaris 2006 model...it does not come with back speakers on the doors this version and i want to put speakers for better sound i have the radio system w13801 it will make difference if i put better speakers than the originals it suppose to have on the back doors?i mean if its more powerfull will it be okay or not????

Sorry for my pure english i hope you understand what i mean....