incoming call ring volume ( sound - silent - vibrate )
I don't think the Audible Touch Tones menu item is actually related, since that controls whether or not you hear dial pad tones when dialing a number.

The setting you want should be CyanogenMod Settings-&gt;Sound-&gt;Silent State, and you'll just need to make sure that it's checked. I have Audible Touch Tones disabled as well, but it doesn't interfere with my ability to enable/disable the Silent State option.