The perceived advantage is that getting the transformers away from the line level signals will result in better noise performance, no AC in the preamp box to contaminate the signal. This approach has merit but introduces the possibilty that noise is induced in the system due to the length of wire needed to get the DC to the preamp.
My personal opinion is that the design of the power supply is much more important than where it is located.
My personal opinion is that the design of the power supply is much more important than where it is located.