Since my Malekko bit is in front of the Xero and the Mobius (courtesy of it's Pre/Post feature) is both in front AND behind the Xero I've tried out quite a few different combinations.
First off, you're definitely right about putting a bit crusher after the dirt. Trying it out before my OD/Fuzz etc the effect disappears for the most part. That said, it isn't super prominent after the fuzz either. For the most part if I'm using a bit crusher after fuzz and before the Xero generally I'm not using the fuzz simultaneously, while when it's after the Xero I do run both the fuzz and the bit crusher at times.
As for before or after the Xerograph/Moog LPF etc it really depends on what you want to do.
I like the sound of it before, as it gives similar results to a fuzz into LPF but with a more "metallic" edge to it. But you won't get the formant filter like sounds using it in front of the filter. It's that resonant peak slamming the bit crusher that gives the vowel like sound.
The bit crushing can also be a lot more prominent when it is after the LPF. One potential downside to putting it after the Xero is that if you have your cutoff set in the audible range but very low (say 100 hz or so) you'll still add harmonic content from the bit crusher. It also means you need one that runs pretty full range (like the Bug Crusher) or else you'll need judicious use of the blend to not cut the massive lows you want.
I probably won't have time today but I could record some more clips to show the difference if people want.