If you make the jump to a suppressor then you'll definitely want to look at extra weight. I'd recommend at least a heavier buffer, I run H3's through my suppressed guns, and then the added weight if an auto carrier isn't a bad thing either. Seems like adjustable gas blocks are all the rage now on suppressed guns, but I run a lot of suppressed AR-15's and have found the additional weight is more than adequate for slowing the cyclic rate.
I'll also say that you'll be surprised at how a .30 can will quiet a 5.56. The hole make be a little bigger, but the extra volume of the can about evens it out so that you get pretty comparable sound reduction within a few DB's. I sell a lot of .30 cal cans to guys buying for the first time who have the same idea as you, and they are always pleased with the results. However, more often than not they're back within the year for another purchase since suppressors have a strange way of multiplying.