Amp and speakers 2005 Radio Sound RG

[Nebraskarider1]

Asking for a friend, looking for recommendations on what is still available and has anyone used to add to the Radio Sound unit preferably plug and play. Or is he just gonna be better off going aftermarket? He would like to add speaker pods to the lowers at a later time so would want something with that option. Kinda out of the loop on the older stuff, lots of options for newer stuff