The 325d, 330d, 335d, 525d, 530d and 535d all use the same 2993cc straight six engine.
It is radically different to your tds - the only things they really have in common is that the are both six cylinder engines and they are both fed diesel.
You probably could fit a different turbo but controlling it will be a problem. Also, the IDI system on your car will not be able to take full advantage of the additional available boost pressure.
Personally I'd accept it for what it is, which is the best 6 cyl diesel in its time and one which still stacks up well now. You could still remap it to 175bhp though and this will stoke the torque up to about 240lbft.