Hi Jeff,
Yes, there is an audio output on that DIN but I think the OP was asking if there was an actual audio jack on the C64 itself and even though there is an RCA RF port which looks like you may be able to take an RCA to 1/4 inch adapter, I don't think that it would put audio into a mixer, although I have not tried this. The splicing you mentioned is a good way to do it depending on the setup. I find that since fitting an audio jack (or two) to my C64 it adds a lot of convenience for me personally, as I use the video out port with a scart cable to send both video and audio to my TV whilst I can just take 1/4 inch audio cables straight to my mixer. For the sake of a fiver the cable I added a link to would be a quick, cheap and easy way to do what the OP is after, without the need for any soldering and modifying, and would work with or without a TV.
Alex.