I have read from people who have listened to SR009 that the phones are more sensitive than SR007. As for the physical dimensions, I think SR007 and SR009 are almost identical. In order to get higher sensitivity, you can either reduce the spacer thickness or increase the bias voltage. Since the bias voltage of both SR007 and SR009 are the same, I am very sure that the spacer thickness of SR009 is less than that of SR007. For the diaphragm to be stable when applying the bias voltage, the tension of the diaphragm must be high enough. The thinner the spacer, the higher tension is needed. Just imagine that with a spacer thickness of only 0.5 mm (my guess), even if some little things go wrong, the diaphragm could very well touch one side of the stators.
Here are what could happen if the tension isn't enough:
1. When you put the headphones on and you try to push the phones against your ear, the air pressure inside the cup would push the diaphragm toward the other side. If the tension isn't enough, as soon as the diaphragm touches the stator, the stator would suck the diaphragm and and wouldn't let go. You can still hear music, but the sound would be distorted.
2. When you play music to a very loud level, especially music with a lot of bass, the diaphragm might occasionally hit the stator and the stator just sucks up the diaphragm. Again, you can still hear the music, but it will be distorted.
In either case, if the loosening isn't too much, as soon as you unplug the phones, the diaphragm would go back to its original position. However, if the diaphragm is really loose, it will just stick to the stator and the only way you can take them apart is to disassemble them.
Of course, if the stators are not straight and flat, that could be a problem too. But, I don't think that is the case.
Anyway, these problems might not be related to what SR009 is having at all. I'm just sharing my thoughts and experiences.
Wachaar C.