Is it possible to increase the volume of a xylophone on a cd recording? Can you separate the increased volume from the rest of the recording?
Whether it is possible or not depends on the recording. If the xylophone is separated from the rest of the instruments in time or frequency then it can be done. But if it plays at the same time as other material and in the same frequencies then it's very hard (inclined to say impossible).
The answer to the second question is yes. If using whatever technique you had a recording same as the CD but with increased volume for the xylophone, you could inverse its phase and mix it to the CD to get just the xylophone.