Hi Phil,
I am still driving the Subscribe/Unsubscribe via the Form Field, so when the user submits an Opt-in, it gets into Eloqua with a value of 1 so they automatically get subscribed to that particular email group, and the same for Opt-out where a value of '0' gets submitted to unsubscribe them from the relevant email group.
The issue is just with the Email Group where we are not able to leverage it to drive it via Form Field where it can automatically drive the subscription / unsubscription request to the relevant Email Group.
So for example, if I have 2 email groups, Newsletters and Whitepapers, I have setup 2 (Subscribe/Unsubscribe to Email Groups) processing steps for each of them where I map them using the "Constant Value" instead of the "Form Field" option and select the respective Email Group.
Hope this helps!