I mostly agree with what Mishmuf is saying, however there are certain points which we must bear in mind.
A xenomorph may be able to scratch metal with its claws, but that does not necessarily mean that it is capable of biting through it. It is easier to scratch the surface of a metal than punch into it, especially depending on the thickness of the object.
The yautja's masks are thick enough to resist small quantities of acid, as seen when Scar marked his mask with a xenomorph's severed digit.
Additionally, we already know that xenomorphs are incapable of biting through space-age glass (bullet-proof or stronger) due to the scenes in Alien: Resurrection. This may or may not have been stronger than the yautja's masks, but considering the fact that the yautja use technology (and most likely materials) outside of our comprehension, it is most likely weaker than yautja metals.
So, despite the fact that a xenomorph may be able to scratch a mask, being able to bite through one, even with that kind of muscle, is fairly unlikely.
However, a xenomorph is definitely capable of punching through an organism's skull. As previously mentioned by Mishmuf, a xenomorph's teeth point outward during the bite, allowing them to pierce the scalp and skull. This, coupled with the punching power behind their facebite ability, allows them to break straight into an organism's cranium.
Just because a xenomorph's facebite is slow does not necessarily make it incapable of such feats. It is still fairly fast, but a xenomorph's head is elongated in shape, and is backed by an extremely strong neck (and body). Therefore, it can be assumed that a LOT of muscle goes behind the stalk which makes the facebite possible. Even if the bite is slow, the xenomorph's powerful neck (and body) would be able to support its head against the pressure which its facebite may incur, allowing it to continue to drive forward and pierce into the skull of its victim before losing momentum.
And thus I clothe my naked villainy
With old odd ends stolen forth from holy writ
And seem a saint when most I play the devil.