You can use the following function available in our source code release to generate eig.nii.gz files that can be visualized on BrainSuite.
function generate_eig_file(L1, L2, L3, V1, V2, V3, outputFileName)
%GENERATE_EIG Generate .eig file. Eigenvalues (L1, L2, L3) &
% Eigenvectors(V1, V2, V3) can be nii structures or .nii.gz or .nii files.
% outputFileName – file name with/without extension (with full path)
As you can see in the description, it just needs the tensor eigenvalues and eigenvectors. The function concatenates these files in a certain way that BrainSuite understands. It should be clear when you just look at this function.