I auditioned both the studio 20s and the 40s before I decided on the 40s. In my 2 chanel system the 40s sounded much fuller in soundstage. Don't get me wrong... the 20s were very nice as well, but the 40s fit the bill for me. I found the 40s sounded best at least one foot from the wall, and better at 2 feet, so you have a valid concern for bookshelf mounting (I used mine on stands). Bottom line, your sub will help the 20s and they would be fine, but if the budget allows it, the 40s would be a nice step up. Good luck!