1. Room
2. Speakers
3. player (dvd, sacd, dvd-a etc)
4. reciever (or pre/amp)
5. amp
6. speaker cables
All in that order.
I've heard a *lot* of difference in how a "player" modifies the sound, therefore, I'll give it No. 3 in importance.
My most important audio is listed.
For video, well, TV is the most