I added a subblock to the IOO model, and gave it a top_names of PSL, so the channels show up as C1:PSL-......
So far, there are just 2 channels acquired, C1:PSL-FSS_MIXER and C1:PSL-FSS_FAST, since those were already connected to the ADC. Those signals are both on the DAQ OUT of the FSS board in the rack. They are DQ channels now too.
So there was a problem with the channel name C1:PSL-FSS_FAST, which conflicts with an existing slow channel. This was causing daqd to fail to start (shockingly, with an appropriate error message!). I renamed the channel to be C1:PSL-FSS_NPRO until we come up with something better.
After the change everthing worked and fb came back.