... and, after looking at the datasets in question and chatting offline, it seems the resolution is the following:

+ the desired, but missing, functionality in viewing these datasets in the AFNI GUI was being able to threshold the stats volume by selecting a p-value. The reason for this not being present in the current scenario is the following:
The stat-to-p conversion in the GUI depends on having stats files produced by AFNI, because we stick the necessary supplementary information of the number of degrees of freedom (and other numbers, where necessary) into the header file. Other software don't include this feature, so it is not possible to have that functionality with externally generated stats, unfortunately. You would have to calculate the stat-to-p conversion separately; there are ways you can calculate this using AFNI programs for certain stats (like Pearson r, t-stats, and others)---'cdf' might be the most useful for that:
[afni.nimh.nih.gov]
---but you have to know the degrees of freedom... Though, that quantity should always be known when computing a stat, anyways, for reporting purposes, too.

--pt