Hi Alexis
Without wanting to dampen your accomplishment too much, I fail to see what benefit balancing the line inputs to unity has with real life recording?
Maybe if you repeat the calibration at a number of differing levels and mark the results with a chinagraph pencil.
The problems as I see it is that a unity calibration will only be of benefit when the levels are set to unity and the source is also calibrated such that you wont need to move the gain on the line ins. Also the actual mic preamps are another gain stage before the line preamp section so they are effectively not calibrated.
Combined with the fact that even a good matched pair of microphones could still give slightly differing outputs. Are you wanting to be able to plug a pair of mics in to the preamp and record a number of sources without touching the gain controls on the Delta 66?
Maybe a better way to ensure the two mics and pres are set to the same level would be to make a test tone or three, low, mid and high frequencies, arrange for them to play from a single speaker. Plug both mics into preamp, set them up in a very close AB arrangement in a dead space in your studio (vocal booth?) and adjust preamp gains untill both channels match (or as close as possible across the three frequencies) then mark gain knobs, repeat for various levels and mark knobs, also note which mic is left/right.