I appreciate the suggestions.
The manufacturer or a modifier can do it internally/elegantly.
I like this idea. I sent a message to Cary and AES to find out what they recommend. I'm waiting to hear from them.
A switch and a few resisters at the power amp input is the fix which the manufacturer should provide.
When preamps offer switchable gain, is it usually a voltage divider design?
Along with Rothwell and Endler, I found
Harrison Labs. The Endlers use Yaego metal film resistors which are about the cheapest resistors you can get. This doesn't instill confidence that they're transparent. Rothwell and Harrison don't say what they use.
I'll wait to hear from Cary to find out what they say. The gain of the AE-3 DJH is 20 dB which is definitely high... especially for me since I've been using passive preamps the past year.