On the A4, theres a boost fitting on the compressor housing, which goes to the N75 valve.
On my hybrid, it has an S3 compressor housing which doesnt have that fitting, so i added that brass barb into the coupler to provide the boost feed to the N75.
If your using stock turbo, you wont need that barb fitting, you'll just need a coupler with the DV connection, which are readily available on ebay.