Upgrade 51824 to 51825 radio

My daughter had a 2007 Prius with a 51825 radio in it (JBL, CD changer). When she totaled that car, I pulled the radio out and we bought a 2008 Prius. This one has a 51824 (non-JBL, single CD). She really likes the CD changer, so I thought I could drop the 51825 into the 2008 car. I discovered the different connectors, so bought mating connectors and started wiring between them.

I have it almost working, but the sound is very quiet and doesn't respond to the volume knob. I'm starting to wonder if there are more differences between the radios than the connectors. Does one contain an amplifier while the other doesn't? The new radio has a Mute connection, so I thought that might be making the sound quiet, but it doesn't seem to make a difference when I connect it to ground or 12V.

Does anyone know if this should work in theory? Are there any wiring diagrams that show how the two should be connected so I can see if I missed anything?

 

That's what I suspected. Thanks for the quick reply and the confirmation. Perhaps I'll see if there is anything suitable aftermarket.