XDJ-AZ & Serato

Hi there.
Using Serato through my laptop, I have a channel one output issue (constant light echo), it's fine with Recordbox, but I prefer using Serato. I can make the echo louder and more distorted by changing the (USB output level) from -19dB through to -5dB, see attached picture. I've also tried changing cables, firmware and software updates, all settings I can think of, but to no avail.

I've also tried your help centre/forum, and I'm now unfortunately out of ideas.

I look forward to hearing back from you.

Colin