I have the D-3 and I installed aftermarket speakers and an amp, plus wiring yesterday. I used the RCA pre-outs on the D-3 to the amp. Now I don't get the audio in GPS mode that tells me when to turn etc. I also don't get that little tone when you change stations etc. What am I doing wrong?

Have you turned VOICE GUIDANCE to ON? your are not getting any audio at all?

It's not a matter of the voice command being off.

I get all my audio (music), but I no longer get the tone when I press a button, and I don't get the audio directions in GPS mode.

I would try to do a soft reset of the unit, just push the reset button with a pin (located next to DVD slot of the unit) for a few seconds. I had a similar issue in the past and that solved the problem for me.