The values are printed on the parts. In general, the way the torque values are stated indicate the intended result. In your case, max torque 6Nm indicates (your torque value) < 6Nm.
Shimano publishes most torque values as: 5Nm < (your torque value) <6.5 Nm. Your stem cap and stem bolts are usually something that don't need constant adjustment once at the recommended torque value, and "topping the torque off" can break bolts and crack carbon.

Setting up your headset is something you usually do once and only revisit if the headset loosens. My stem caps are only tightened to bottle-cage torque, or 2-3Nm, and that's just to keep the bolts from working loose.