lmao! I dunno, I got into car audio over 20 years ago... and granted I didn't have cell phones and mp3 players to need an aux in way back when, but with the aftermarket stereos I've had and stock head units in cars that have had aux in, plus popping into friends cars, it's never once been an issue. Even with the RAV4 stock head unit. I'm honestly surprised to find you are having an issue. I could see one device not having a high enough signal, but multiple? I've also hooked up rca cables with a headphone jack to the line ins on my (high end) home stereo, the receiver at my trailer, and into a ghetto blaster; as long as the volume was max on my phone or ipod I have no issues with volume. Best of luck getting it sorted out, it's a shame you have to resort to an add-on piece just to be able to enjoy your music!