I Don’t think you can add an amp to factory speakers w out getting into redoing the entire system! I do know that Crutchfield sells replacement speakers that are direct bolt in w adaptors to make them work made by Jl Audio , i blew my driver door factory driver and order’d thru them but Nvr installed em as i got the feeling from the Crutchfield Rep that the factory speaker will work and sound better , ended up going to dealer and he had one in stock for $110 so i just ret’d the Aftermarket ones back to Crutchfield
I have a 15 and a 12 before that and in both my Bitch’s they had the HK ^^^ and the system Is Very loud and Clear rt up till vol 38.. Where i felt it lacked was the bass dept..
I added a Kenwood 600w amp and a 12’ JL ported Power wedge in the trunk! This setup Slam’s like i mean Slam’s!!
Wasn't bad in terms of price , got thru crutchfield somwhere round $1400 for the Box , amp and a Power wire fuse block kit.. Also a lc2i to interface for signal. Did the install myself in garage took abouts 4.5 hrs w a careful clean take my time install. If your not somewhat mech inclined to do this type of Job
A competent Stereo shop will do and charge ya $300 tops.
I even installed a Gain control for the basss for those times my Girls bitxhy or i have the Rents or kids in My Rigg!
If you search my threads you’ll see my system and install pix!