Ok, so I tried a lot. In the original, I could only marginally improve the quality.
The hair meshes have some very sharp angles and can also become pretty dense, depending on the POV.
Setting the filtering mode to bicubic is advisable for such a thing and you get a few more clear pixels but that doesn't solve the problem.
Same goes for translucency. (btw leave out that c4d backlight shader as it won't help you. translucency already does the job)
The normal tags and phong tag's settings don't seem to influence it visibly and can be removed.
I also tried different render settings, changed the AA types and radii, increased the max depth, GI/AA ratio, etc. etc. Didn't really help.
It actually seems that there's some issue with the volume scattering with those very fine, hard alphas. Though it seems to depend on the angle and resolution.
If you do a close up of the affected areas, there shouldn't be any problems. So a (much) higher resolution might help.
Also, what does work is to manually add fur, even when it's very dense(flat geo). I combed it a little bit and it looked fine.
That would be a way to solve the problem and it would look a bit nicer imho. It's not that much fur you need to worry about so it should be done in an hour.
The best solution would be to mask out the fur when rendering in the volume and add it back in post. A direct light solely for the volume would be better.
I bet I forgot something...
Anyways, I'd be interested if someone else has a solution for the problem.
