It doesn't look all that different, but the first image didn't have that much lit up in it to begin with.
This is totally cool! You can see that the OSEM lights are almost entirely gone in the subtracted image.
Can you switch to trying with one of the *TM*F cameras? (ITMXF, ITMYF, ETMYF, ETMXF) They tend to have more background, so there should be a more dramatic subtraction. Den or Suresh should be able to lock one of the arms for you.