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 smile
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Nert's Home Theater---
Mostly electrically driven box-shaped things (with dials and buttons) connected by wires and cables of various colors, diameters and lengths.