Hi Peter,
I also captured the spectrum of Alhena with a Star Analyser (SA200 in my case). My result is attached and is in pretty good agreement with your own. I wonder if you should also have a play with the focus to see if you could capture one or two more of the Balmer lines at shorter wavelength? I use an Atik 314L camera and I process the images in BASS. I like the BASS alignment function for stacking the images, it seems to do a good job on aligning the Star Analyser images when the star can shift slightly in position from one image to another. Anyway I think your results are looking very promising
Cheers
Hugh