3. CD Players
Most peoples' music collections contain primarily CDs. Some people have an affinity for vinyl records (or possibly even tape cassettes), but for the sake of expediancy, we'll begin with the CD player.
Your hi-fi system will have to meet a number of criteria which will probably include: affordability; aesthetic appeal (although this will be more important to some than others) and, perhaps most importantly, ability to replay music accurately according to your musical tastes.
Every CD player (whether intended or not) will have its own "sound". This loosely descriptive term encompasses its character. When you listen to different players, you'll find that some are more "laid-back", some are more "forward", some are "brighter, and more aggressive", while others can be "ruthlessly transparent" — meaning every highlight and detail is replayed including every imperfection there might be in the recording.
When you audition players, listen for soundstage transparency. The CD player will have a significant effect on this quality. The player's objective is to replay the performance, not its interpretation of the performance. The soundstage and imaging should have an "airy" or "open" feel. If you feel compelled to just sit and listen to every CD in your collection, you're on the right track.