I spent a lotta time on this in the Aughts, and ultimately gave up. IMO trying to simulate Velvia is just as fruitless as trying to simulate Kodachrome. You can get some of the flavor, but compared to the real thing—viewed with rear illumination, whether in a slide viewer (not projector) or through a loupe on a lighttable—it tastes pretty weak. Scanning the real deal and displaying the results on a good monitor or TV gets you closer, but still the 3D nature of the image in the emulsion is lost. As is much of the tonal subtlety.
Note that all this also applies to prints made from transparencies. I rarely had transparencies printed pre-scanning…and then after getting my first scanner rarely printed tranny scans.
Digital color is just different. Some things lost but other things gained…as is typically the case when media, tools & techniques change.
-Dave-