Hi Chris,
I'm in exactly the same boat as you. I trade the ES and YM using Ninja, but have been looking to trade the SPI (Aussie 200) using Ninja. I have been told that the SPI volume is very low and this is an issue. We would be better off trading the DAX or Nikkei using Ninja as the volume is a lot better.
When you have a solution, please advise and vise versa.
I once received a quote from Halifax, however I will never use them again, so this is not a solution for me.
Happy trading