If I understand the original idea behind this thread, the idea here is for pirates to be attacking starships to get at the tantalum in the warp core, so they can sell it to someone who will use it to make a warp core for another ship?
Oh, and turn a profit in the process.
I would think the pirates in question would instead carry a prize crew with them. Method of operation then would be to sieze the target vessel, imprison or space the troublemakers from the target ship's crew, use their prize crew to man/supervise the prize vessel, and send the whole ship off to the black market.
That way, you get whatever cargo it was carrying, the net hull value of the ship itself, and the tantalum (in a usable form of a working warp core).
What they do with the rest of the crew upon vessel siezure or upon delivery I suppose is a commentary on the pirates in question.
The chief problem then is taking the other ship in a more or less intact state. Also, the last thing a pirate crew really wants is wreckage floating around to let the authorities know they are operating where they are. Far better for the target ships to just "disappear".
Its a thought anyway.