That is where the catalytic converter is located. If you are riding normally and its glowing red hot its possibly plugged. Are you sure its running on all 4 cylinders? A misfire will shoot unburned fuel into your exhaust and melt your cat. Also like you said the servo could be stuck shut. I'm not sure how the servo works on the zx6 but on my s1000, you could hear it open and close when you cycle the key. I would remove the muffler and the pre-chamber and inspect. This is not something you want to put off either. That could very easily start your bike on fire at a stop light.