I've not seen one either but the internal fixings could be screws or nuts on captive bolts (my guess M5) and the best tool would be a ratchet socket with 1/4" drive. You can get these here from RockBottom type shops very cheaply. Not strong enough for car work but plenty so for 'tronics.
If you DO have to de-knob the mixer, need I tell you to take multiple photos first? And, I don't know if that particular mixer uses an outboard PSU but if so I think you will find they are a bit feeble and not easy to replace? In short, take some voltage readings while it is working so that you can build/have built a new one.
Lastly, if Mr Sweetbeats has ever been afront one you will have a good friend there!
Dave.