I'm slightly embarrassed to say I've never tried it, but if you have a recording on your 60d that has levels you are satisfied with, perhaps you could play it back and send a feed to the camera to determine the appropriate level of output on the 60d and the level of input on the 3200. I don't know if the 60d outputs in playback or in recording mode only???
I didn't find any specific discussion of the 3200 input gain. I did find some posts elsewhere suggesting an input level of 6 on the D800, but that's a higher end and different model.
If you have a dynamic poetry reader, you could be trying to record soft spoken words one second and near shouting the next. It is difficult to set levels for this.