Why would you even want to mess with a new head unit and third party control adapters? Not sure which Elantra model you have but the 2013 coupe has a very good head unit with an internal base boost and a pretty good kick to it. I just replaced the factory speakers with the Infinity 6030cs speakers (the kit includes integrated tweeters) and WOW what a difference. I was going to go with an amp as well, but didn't need it after hearing the sound with the new speakers. If don't have the coupe, adding an amp (and speakers) to the existing head unit will cost you less and make a huge difference that I don't think you will be disappointed. IMO!
Good luck dude!!