Normally if someone says that it cant be done then that is like a red rag to a bull and I try to come up with a solution, but now you have brought steel into the equation then I would agree with the others that it will be really difficult as the requirements are at opposite ends of the spectrum.

If it was Diy the you could compromise on the design and use the machine to the best of its abilities but you seem to be saying that it will be a commercial use so that wouldnt really be feasible.

If you did proceed you will need to two spindles.

1. Low speed with high ridigity and power at low speed for steel.
2. High speed and power at high speed for ali.

You would then need 10mm pitch ball screws on high power servo motors with high resolution encoders to get the accuracy. Etc etc.

It can be be done but like the others have said it will be expensive and you will still end up compromising the design. It may well be cheaper and better from a production point of view to build 2 specific machines. Good luck