Unless you are adding a sub, it's fine and sounds goo just replacing the speakers and head unit. Then later if u add a sub you can run the RCA cables from rear of stereo to the back for sub and the amp for the sub. Your aftermarket stereo should have built in cross over so te infinity amp will run stock speaker locations and act as mids and highs while ur bass goes to sub. Has worked for 12 years in mine.
1995 JGC Limited 5.2 v8, black with gold trim
1976 Olds 98, 82 Olds 98, 84 Olds 98, 89 Trans AM