Hi Salvatore,
I think we'll need to add support for these data formats to yt itself.
Before we moved to github there were some attempts to add support for more ramses fields in these pull requests:
Unfortunately none of those efforts proceeded to the point where we could merge the code in.
If you'd be interested in working on this, I think it would be a great initial contribution to yt.
If you're not interested in adding support for this, then we could at least open an issue to track this feature request:
It would also be nice if you could include some sample datasets that someone who is interested in working on this but does not have access to ramses-rt could use to debug with while working on this feature.
In the end yt's support for data formats is limited by what sorts of data the developers who have worked on any given part of the codebase have had access to. Unfortunately given the culture of astronomical simulation codes, that sometimes means we do not support all possible versions of a given data format simply because we were not aware of that subset of the data format when we initially added support.
Hope that helps,
Nathan