Sound only, no bass

it would help if you included pictures of the installed amplifier so we can see the connections you made and the final amplifier settings you chose.  Be sure to take photos that let us read the position of each dial. From your question i can't discern if you mean that you hear vocals from the sub or from the other speakers in the car.  Is the sub playing any music? 

step one: no amp is set "from the factory".  every dial needs to be adjusted for your vehicle.  In the image below i added green lights where I recommend you start.  If you're not sure where the dial is pointed, go fully counterclockwise then rotate clockwise to my suggestions below.

Gain: keep this as low as possible

Bass Boost: keep this as low as you can, using some is OK if you boost at the amp and cut bass at the head unit (to remove bass from speakers)

LPF: this is what removes vocals from the sub signal, you want it around 80Hz

Subsonic: this removes low bass from the speaker to protect it.  Not needed with a sealed box but you're safe to use it between 10Hz-20Hz.

Phase Shift: this is adjusted until the bass seems to blend with the speakers in the car.  You'd need specific music selections to listen for when the bass seems to come from the front speakers and not from the sub behind you.

If you've tapped the front speaker output through a LOC (which LOC?) then you should get volume control unless the gain and boost are set too high.