I have both at our warehouse and the 6.2's are a good bit louder.
You can add brackets to the 6.2's through the terminal cover where you will need to take the 4.2's entirely apart.
Raul (someone post his website) has brackets that people have used, there are some links at
www.diyTower.com and we are tweaking our "BYOS Brackets" (bring your own speakers) more info at
http://www.monstertower.com/accessory2brackets.html