what encoder can take advantage of 16-core setup? converting bluray to mp4

I'm thinking of upgrading my 6-core setup (single CPU) setup to a 2x8-core/CPU setup. I'm wondering what software will allow me to fully utilize all the cores.

I've been using handbrake but I do not think it utilizes all the cores. I prefer software that is freeware but paid software is ok too if it's not to expensive.

Thanks!