Modular SGDMA - Doubt on Target Address

The master settings are in the master IP core(s). I wouldn't recommend changing those settings until reading what they do. There is a .pdf that documents each of the cores that makes up the DMA.

You can put the read DMA into a loop. I just mean if you want to transfer say 16MB, you can always break that down into 16 1MB transfers (that's the "normal" way to use a scatter gather DMA)

I have no clue about the target address changes causing problems. I would study the host code to see how it works, it's possible that by changing the address you are accessing invalid locations and that would be a problem.