I kinda came up with the same idea a while ago, but back then I didn't know what I know by now, so I will give it a second shot.
Yesterday and today I tried to set up automated muscle firing (before I just hand-keyed the excitation attribute, just for testing), but the lines of action seem to really not work out for me. When I set up the line of action so that it follows the bones and then attach it to the zFiber everything seems to work fine with the default settings. The fiber colors change to yellow as the arm flexes, but as soon as I change the strength or the exponent the it gets completely ignored and the fiber colors stay red. It still gets excited though, but based on a strength of 12*103.
I always cleared the cache so that's also not the issue.
For me it also seems to be very inconsistent when the zLineOfAction shows up in the channel box inputs of the fiber and curve. Sometimes it's there, sometimes it's not, but it always shows up correctly connected in the Ziva Scene Panel.
Any ideas what's causing this? Did I miss any details?
Would be really glad for some advice.