There are various military, civilian, remote or manned underwater vehicles that can undertake recovery from depth.
Of course. We have all seen Titanic. there are small capsules that can be sent down to depths in the Mariana's Trench. But I'm talking about a salvage operation- not just a documentary for Wildlife on One.
As far as I know, there is no apparatus that would be able to salvage an engine for example sitting at the bottom of the Atlantic. The TWA wreckage was salvaged quite well due to its relative proximity to land. But this is different.
My educated guess would be to purely focus on the FDR and salvage that.