RCA to 1/8" would be my vote.
But just because it hasn't been mentioned (yet / or I missed it), you could do the 1/4" to a headphone preamp and attenuate it there. You'll have to set the headphone out really really low. Or if the mixer has such an output, with knob, use it. Not ideal as you'll have to run at about 0.5 of 10 on the volume output(5%, maybe 10%). Also vulnerable to cell phone handshakes once you get to the thin cables and unbalanced output like that. But the RCA cable will also be vulnerable. Assuming that the little plastic voice recorder isn't also vulnerable. And depending on the quality that you need / want. Lots of options to get something. Depending on what you have versus what you need. And what compromises you can live with. And if you have any time / option to do any trail and error beforehand.
When I need something cheap, I generally take the headphone out and turn the volume way down. But that's mainly a content over quality scenario. Which is far from an common or ideal circumstance. But for judges tapes when no one seems to own a tape player anymore. An option.