Hi Trevor,
Yes, you could substitue shrugs, lateral raises and front raises for the shoulder press. And tricep extensions since the triceps work too. What I dislike about shrugs is that most people tend to hold tension in the upper back/neck region causing the muscles to become short and tight, and should really be concentrating on stretching that area versus hitting it with weights. So, proceed with caution. I'm not saying you shouldn't do them, but am wondering if the heavy pressing with the Cybex has over-stressed that area.
I suggest free weights for the exercises above. And remember, as Cathe states in one of her videos about shoulder work - "arms elongate, shoulders contract". VERY important cue! I often see people who use free weights for their shoulders lead with the upper back (traps) to assist with a heavy weight load. Better to lighten up and keep form very strick to avoid any injury to the shoulder joint.
Be sure to do enough back work (rows, rear delt flies, etc.) to balance the anterior muscles and you should be on your way!
-Roe
