You cannot turn off SRTP. It is part of the standard and it will probably never be removed.
The key is exchanged in a DTLS key exchange and will be that way for a while as Mozilla and Chrome are in agreement that it is the best and most secure way to exchange media.
That fingerprint is not the key itself, the key is exchanged via DTLS, you can actually see the DTLS exchange if you listen with wireshark on one of your machines so that you can see what is going on with the exchange.
You will need to implement a breaker to interface with the webrtc client and the SIP client. SIPML5 already has a breaker in play.