Just remember that normal rules are trumped by special rules. Special rules are trumped by codex rules. The codex gives two quite specific rules about the weapon that POTMS doesn't affect. This is not "normal permission". This is codex specific permission on when you may fire the weapon. Additionally, as stated above, you cannot fire the weapon at your full BS as you must fire it indirectly.
For example take this example:
You move the Deathstrike in 6 inches from reserve. The rule book states you can fire one weapon at your fulls BS and snap fire every other weapon. However, the codex forbids you from firing as you have moved. You now put POTMS onto the Deathstrike. You can now fire two weapons at your full BS (one at different target), but the codex still FORBIDS you from firing the weapon as you have moved and you can't use POTMS to fire the weapon as you can't fire it at your full BS.
Sorry, but your bypassing things just to make yourself right. Rule states it cannot fire if it moves or in turn one. Those are the restrictions when you are not permitted to fire.... the two restrictions for POTMS are either flat out, or popped smoke. neither of those occured, Thus you may fire an extra weapon, which, as you get to choose, can be the missile. You would roll with usual modifiers, and if you get lucky, fire it.
No where in the rules for deathstrike does it say that POTMS does not effect it. In fact, considering your also trying to use indirect fire as a reason, I can move and POTMS something else that fires indirectly..... why not in this case? Yes, your given 2 specifics that would NORMALLY not allow it to fire.... but neither of which match up with the two specifics that PREVENT POTMS from taking effect.
It can fire, its cheesy, its annoying, but IT CAN FIRE RULES AS WRITTEN! The fact that so much of a twisted argument is needed to even try to prove it otherwise shows that 1. it needs to be FAQ'd for people who will go so far as to argue it out like this, and 2. Your grasping at straws to try and prove the point, and ignoring the facts and wording of said rules.
In short, You can fire because : while you have reasons the deathstrike is not normally permitted to fire (moving, first turn) they do not match up with the 2 reasons given in the POTMS rule that prevent it from taking effect (flat out, popped smoke) thus, the rule takes effect, and allows you to roll to fire the missile.
