6" trees are not a light duty job unless you are running heavy eqpt. For a 30hp that is a asking a LOT. I would not recommend using a front cutter on your machine for anything like that - when u raise it where is the discharge headed? Even a rear HD cutter on your machine is not going to work well for that size tree. You also need to see what your hydro flow is before even thinking of a mulcher as most the small tractors don't have a whole lot.
Mulchers are excellent at clearing land but I have never found any around here in that price range, mostly they are far more expensive. Heck, you can spend over 2K on just the teeth.....