It's surprising how common this problem is. I have to wonder why manufacturers design preamps with so much gain. Five or 10db should be adequate for most systems. The 21a is rated at 17db.
I used 10db Rothwell attenuators to tame my preamp and it worked to some extent, but I never had the kind of control for low level listening that I wanted. Maybe 15 db attenuators would have helped. I don't know.
For what it's worth, I had a similar experience when I contacted Belles about a problem with a 150A. No response. Fortunately, my problem went away without needing any work, but it bugged me that David didn't seem willing to help. Yes, he's in business to sell gear, and he probably doesn't have a lot of time for non-revenue generating questions, but companies that stand by their gear get rave reviews from customers and those raves usually lead to sales.