How do the normal bookshelves compare against surround speakers?
Let's take an example of something like JBL 530 vs Klipsch RP-402S....or JBL 530 vs Airmotiv E2 / E2+
Both the Klipsch and Emotiva E2 are going to have less low end output than the JBL 530. Sound wise if you have JBL in front then would be good to have them in back if you can fit them. If you need a wall mount then I'd go for the E2/E2+ due to the tweeter being a bit more neutral.