CD Transports
The transport is component responsible for reading the CD, and then making that digital stream available for conversion into an analog signal by a D/A converter. With integrated CD players, the transport and DAC sits in the same housing.
With separate Transport and DAC combinations however, you have the advantage of more flexibility and also several technical advantages that come with each device being dedicated to what it does best.
Reading the CD properly to get as much of the music as possible is vital, and a good transport is essential if you want to get the most out of your CD's