My understanding is it's a simple padded input (6 db, perhaps?), though I'm no tech so perhaps others will chime in with more specific info. Many types of gear have available padded inputs, e.g., most PAs (for regular and condensor mics), acoustic guitar amps (passive and active PUPs), and of course, electric guitar amps.If you Google "twin reverb second input" and/or "amplifier padded input," I'll bet you'll find lots of discussions. What I'd do in your position is take 5 minutes to experiment with yours and listen. This will tell you more than anyone else's descriptions.
When we Go to Heaven, will Jer ask whether we were the perfect Jerry ... or whether we were the perfect us?
What does Jerry tone mean to you? Copying Jerry slavishly? Honoring Jer's music no particular way but our own?
We're each of us unique. And also the same. Can we open our hearts and minds to both?