the reason why you're having a problem is because the AD-20 provides a minimum gain of 17dB. I'd also recommend getting a set of attenuators. Actually, I have a pair of Shure A15A5 attenuators that I could let go. I bought them from someone on this site, back when I was using my AD-20. However, I haven't used them in a many months, not since getting my V3. shoot me an email if you're interested.
Jason
jasonsobel@myway.com