On the content side, I like pcm wav files. Some people prefer FLAC. You want as little compression as possible or no compression at all. Uncompressed audio files are huge so you will want adequate storage capacity also. Once you have content you will want to improve your playback and listening devices as needed. A stereo headphone amplifier sound-card or external DAC with a nice pair of studio headphones. Some people like the noise canceling headphones. I prefer a quiet environment with an open ear design and a nice pinot noir =)