The absolute best source is the official Audi ErWin portal. For a small fee (approx. €5-€30 for a 1-hour access), you can download genuine, factory-original Stromlaufpläne. This is the standard.
The most accurate diagrams come from KFZ-Verlag or Originalanleitungen.de . These provide the original Audi workshop manuals in PDF format for specific year ranges (e.g., 2000–2004 or 2004–2008). stromlaufplan audi a4 8e pdf downloadl top