Rodney- there are a couple of factors that the trim pot can't help with. *Those are:
1. *Body woods/construction
2. *Pickup type/design/output
You're right when you say that the extra copper in the 7-string p/u's affect the tone and/or volume. *They most certainly will. *I'm not sure if you can get identical tone, but I can get your output level closer.
When you open the electronics cavity on the DE-
equipped guitar, look for a little white-faced volume pot. *It's one of the flat ones with the tiny arrow that points to it's setting. *That is your gain adjustment for the piezo output. *It will
NOT change anything regarding the
magnetic pickups (even if you've done the KJG Wiring Mod). *You'll need to do some tweaking with the guitar(s) plugged in, but you should have comparable (if not matching) piezo outputs in under 10 minutes. *
To get matching outputs from the magnetics on each guitar, you'll have to shop around DiMarzio.com and find matching 6- and 7-string p/u's.
Psssst- Tone Zone & Air Norton in the 2020 would f-ing rock. :-)