its actually a mistake to replace your 12pt wrenches with 6pts... adding some 6pt wrenches would be fine.
for a 6pt wrench to work, you need a whole ton or room to swing the wrench, and if you are using a wrench, id bet you dont have a whole ton of swing to begin with. there is a reason 6pt wrenches are not very popular, and all the rage.
the fact is, modern 12pts do not round fasteners like they did before the change to "flank drive" style broachings. unless the fastener is already damaged by someone using the wrong size, it will be very rare that you round a fastener with a 12pt. they grab the same amount of material, and the same spot on a bolt head, plain and simple
take a few minutes and have a look at these two threads and the pictures included. it shows how sockets of different makes and styles grab fasteners. you are guaranteed to be surprised at the results, especially how the "top" brands perform.
socket contact points
http://garagejournal.com/forum/showthread.php?t=73245
wrench box ends
http://www.garagejournal.com/forum/showthread.php?t=59707