You will be able to upgrade AUDYA 4 and 5's memory regardless of if you have the AJAMSONIC upgrade/package or not, so no, you do not need to have the AJAM upgrade before you get the RAM expansion, but it will help to have it.

It will be available on one of the AJAM options so in that case, you won't need to purchase another memory expansion card again.

Sokratis is on the right path with regards to the upgrade mentioned above - however the memory package compatibility for each unit will depend on it's seial number.