Many good answers above. On the basis of sound quality alone it depends on if you like the sound. Of all the one brand systems I have heard there were not many that were outstanding. It is very difficult for any one manufacturer to design one very good component let alone several. I prefer to mix and match. It is more difficult and time consuming but can yeild superior results. It can also be frustrating some times.
Benefits of brand synergy
How important is brand synergy in matching components? This not only includes amps and preamps but also digital sources from a particular brand, say Arcam or Kell. Is this "synergy" important just for impedance purposes or is there an additional sonic benefit of having everything matching? Thanks.