Personally, on the 2.4, I don't think those resonance boxes will make much difference (if any). They are designed with the 2.2 litre petrol model in mind, the exhaust pulses on a turbocharged diesel engine are completely different.
The thing I found with these on the 2.4 is that the engine doesn't get the exhaust system warm enough to get the full noise benefits. I've noticed after a DPF regen (mine still has DPF) that the exhaust note deepens when the exhaust is hotter. Otherwise, it makes only a very subtle difference. However, the performance difference is there, they have a much better flow and it feels better at low RPM's (although I have no rolling road evidence of this) Overall, it's a good upgrade for the 2.4.
Gone but never forgotten: Alfa Romeo Brera 2.4 JTDm 210 SV