Just tried that, didn't work. Luckily, it isn't a big hassle to unplug the speaker wire to use the RCA outs.
It is funny - it seems like sometimes the people designing stuff have no idea how it would actually be used. I bought a 2015 Mazda, and the radio would play mp3/m4a files on a flash drive. However, it would not remember where it was when the ignition was turned off, it would always start back at track 1, AND the "random" feature would follow the same path every time. I reported it to Mazda, both US Operations and my local service department - neither had heard of the issue. Fortunately, Mazda HQ was quick to work up a fix within a month.