One of the things that the modification people are replacing are the output OPamps chips in the analog section of the CD-player/DAC. These OPamps are often of inferior quality. It is better to replace those OPamps with good sounding ones or to use discrete OPamp modules. What is rationale of using the most advanced DAC chips and algorithms but to implement cheap bad sounding OPamps? To those "high tech digital audio" manufacturers: We (audiophiles) are interested in sound, not technology!
Chris
Chris