Digital Audio ICs
What you want is called an Audio Codec, Audio A to D, or Audio D to A.
The Audio Codec is a Audio to Digital converter and a Digital to Audio converter in one chip or module.
The Audio A to D, also called Audio A/D, is just the audio to digital converter chip or module.
The Audio D to A, also Audio D/A, is just the digital to audio converter chip or module.
A good example of a Stereo Audio Codec IC is the WM8731 (about $3-$4 single quantity from mouser.com in US). It is a high quality 16-24 bit, 8-96KHz sample rate audio encoder/decoder that uses a I2C or I2S interface and has a stereo headphone amplifier built-in. It is used mostly for audio and made by Wolfson Microeletronics(wolfsonmicro.com), they also make Audio A/Ds and D/As and other audio related chips.
There are many other manufacturers of audio converter chips like TI and Cirrus Logic to name two.
These chips can range from around $2 to $30 US per chip depending on number of bits, noise, distortion level, number of channels, and extra funtions.
Hope this helps you.