So Emre...bottom line:
 

You can use the Y connector I suggested above with your DXA-6 to record your AT4073 at different levels in two channels. To respectfully summarize what the pros have added, a good mixer is a better choice than this technique, and 20 dB is way too much of a differential if you do use this technique.

I certainly was not expecting such an educational discussion! I hope someone else learned something too.

I thank every participant.