I have tried XSVCD compatibility with one XSVCD's downloaded from VCDHelp on the 10:th of July 2002:
The same thing that happens when I try VCD's happens here, the player first displays , then it gets blankfor a short while. It then displays , then the screen just goes blank (blue). If I press "PLAY" on the remote control, the player immediately shows on the screen.
The same thing happens if I have the XSVCD's on CD-RW media.
As I don't have any EuroLine 6620 with VCD/SVCD capabilities, I don't know how it works with XSVCD's. But it will probably work about the same as my United 3155.