Hallo!
quick tanh looks good. i put in a dollar and my cpu gave me 96 cents change!
I did not follow the whole thread, so maybe this was already said.
But I would also do the tanh interpolation with a wavetable. You can simply once use this function to generate the wavetable and then use it and it will be very fast (and you can use any function you want)
too ...
LG Georg