Dimitri, I was honestly about to ask the same question! I am in a similar situation as I am getting ready to install my dosing pumps in the cabinet.
My idea was to use the kalk stirrer as the main source and two part to compensate for the difference. This way, I use up all my kalk and will not have to use as much two part (please tell me if this is risky)
As a side note, I noticed in a youtube video that they use vinegar to help dissolve the calcium in kalk solution. Adding some vinegar to the DI reservoir will keep the calcium dissolved and helps neutralize the pH a little.