WELCOME!
It sounds like you have a really great start on a bad case of O.C.C.D. that I'm sure will be all consuming once you have heard the difference between the unmodified C-4000 you enjoyed and the BillD modified C-1. I believe the C-1 to be a cleaner more musical sounding preamp to start with, but the BillD treatment lowers the noise floor to such a degree you will be astounded.
I have also become extremely enamoured with the modified C-1 sound and the significant work of it's engineer (BilldD) as well as the many fine techs here on this site who have learned to duplicate and build upon that genius. I also have a C-4000 in the process of being modified and look forward to hearing the transformation it will surely undergo.
I look forward to hearing your review and opinion of the BillD modified C-1. I have said before that adding one to your system is like getting an all new and better sounding set of gear.
As our good friend Zumbini would say.: "Enjoy the music!"