I have not heard the 4.5 upgrade. In speaking with Allen Wright, he says that the scd-1 with the 4.5upgrade gives the player much more resolution. More air and space between the instruments, along with more depth. I have a friend that has the dac6/emm setup. Allan told me that I should compare my scd-1 with his setup when I have the 4.5 upgrade done. He is not saying that the scd-1 will sound better, but he feels it would come pretty close. For $400 to $500 investment, that sounds pretty good to me. Allen posts on Audio Asylum. If you go onto the sacd board, you can ask him about it.