It should work as follows:
Each torpedo marker counts for 1-6 torpedo's. In the event that a salvo of greater then st 6 is launched, place down two markers side by side. Each token must be consolidated to maximized in strength to the strength of the salvo. For example, A Desolator fires a strength 9 salvo, Two tokens are placed on the ships base, one is st 6 and the other is st3 (you cannot have one 5 and 4). When strength is reduced, you always reduce from the lowest strength token first.
Example: The Desolater fired it's torpedo's at an imperial cruiser, and scored (luckily!) 4 hits, reducing it's strength to 5. The strength 3 marker is removed, and the strength 6 is reduced to strength 5. The single marker continues on it's path to it's maximum movement. You DO NOT reduce the strength 6 to a strength 2, and have two markers for a strength 5 salvo.