more on my own question:
after speaking with a chemist, he explained to me that the sequestering agent will tie up any free metal ions in the water, including copper or silver. Yet, silver will still maintain some sanitizing ability, due to the electron charge of the ion (or something like that, I'm not a chemist!) It was his opionion that the mineral purifier will work, even if you are using a metal sequestering agent.
Therefore, even though the MetalGone or Minquest is tying up any metals to prevent them from staining the shell, silver ions are still available in the water to kill bacteria and viruses.