Ah yes, this :) So I guess I'd chalk this one up to the overly simplified C4Ds way of handling these things.
From what I know, and I could be wrong you only have one option - The projector shader. It should pretty much do what you want it to do but with three major minuses.
It will ignore whatever UVW settings you have set in your tag which is OK but whenever you'll want to edit this thing you'll need to dive deep into your shader tree (presuming you are using the node editor, otherwise I think you'll go crazy). To me working with the projector shader is just a really great way to get lost when building complex shaders.
The second minus to me is that you can't preview the darn thing in the viewport. You'll probably have to plug the projector shader directly to the diffuse slot to see it in the viewport so that you can edit the scale / mapping. The IPR afaik still doesn't show the projector shader properly (it just shows a black color instead of the texture).
Octane for example does things a bit better. It offers you a projection & uvw transform nodes that you can use to adjust the texture much like a projector would. The big pro imho is that the uvw transform / projection nodes still respect the original UVW tag so that you can scale / rotate or whatever the material as a whole if need be. The projector shader just tends to override everything if I remember correctly.
The third minus would be that you can't assign a single material to different UVW tags on one object where you'd control how each gets applied to separate polygons. Don't think this is possible in C4D at all but I guess I could be wrong.
3ds Max solves the entire thing in a better way in my opinion. You create another UVW Map modifier (in c4d terms a tag) and you simply select which ID Channel it will have and you just need to make sure that the texture has the same ID. You can then always edit the UVW Map modifier (move it around if needed or just adjust the scale, rotation) or even stack them up and its always there in the modifier stack. What is great is that you still keep control over the texture itself because you can still control the PSR of it. Also, you can assign UVW Map modifiers to certain parts of the mesh and so you can imagine it allows for some fairly advanced workflows. I suppose I'm digressing with this part here but I suppose I hope this gives the devs a better perspective into things...
I'd be really excited to see multiple UVW channels / IDs implemented. Definitely a +1 although I'd like to +1 to Maxon as well :)
