Hello, I'm sorry you haven't received a reply sooner, I hope the following assists you.
Firstly I wouldn't say the injectors failing would cause a whooshing noise, the only thing that the injectors would do to cause a noise would be if the sealing washers failed, this tends to cause a ticking noise but it wouldn't leave a boost pressure concern.
As there is a noise this would indicate that there is a leak in the pressurised side of the turbo system. Although the pipes have been checked have them double check that the metal pipe near the gearbox hasn't cracked where it bolts to the gearbox as it's quite common for this to happen. Also check that the turbo itself hasn't failed as again this is quite common on this engine, remove the air intake from the turbo and check for play in the turbo and any sign of damage to the impeller blades, make sure it hasn't seized (unlikely due to the noise).
Removing the DPF can cause concerns as the turbo system on this model has an intercooler bypass that operates when required, check that the flaps inside the throttle body move as they should as if one is open at the incorrect time the boost pressure can be lost.
Check to see what the actual boost pressure is reaching and also if the MAP sensor is reading correctly.
From the description you've given this is a pressure loss in the boost system, this is why you hear the noise as the air escapes somewhere in the system.
Start with these points, let me know if I can assist further or if you have more questions regarding this and I'll reply as soon as I'm able to.