It has been awhile since I last read about this salvage operation, but I seem to remember that their latest method involved using some high-pressure jetting technics to create the channel to the deeper water.
I once worked for a company based out of Singapore,
BaySea Cable Systems, that was involved in lots of subsea burial of gas pipelines and fiber-optic cable thruout SE Asia. We concentrated on the shallow water 'beach approaches', where it was deemed necessary to insure a good trench was available to bury those items and protect them from damage particularly by fishermen.
We were also tasked to remove some clay like sediment from a power plant water intake facility with our special water jetting equipment.
Since our jetting equipment was proprietary knowledge I will not mention those details unless, or until, I receive the okay from the owner of the company. I did bring this subject thread to their attention in case they decided to contribute.
Brian