On what do these small changes accumulate in the first place?<quoted text>
Your example is not related to the issue at hand. The mechanisms of "microevolution" and "macroevolution" are exactly the same (do you need me to review them?). Accumulation of small changes add up to big changes.
This is another straw-man. You seem very fond of them.
Secondly the small “changes” you refer to more likely are fatal or neutral mutations in which case the organism goes nowhere and the changes do not accumulate
Other small changes may be expression of allelic variation
In both cases
DNA was present to begin with
Nothing new has emerged
So the process you are desperate to validate ---evolution----never occurs