As a followup in case this is helpful to somebody else, I needed to convert my sequence to RGB before it would allow me to export to JPG and PNG. I'm assuming because this was a multi-tiff file where each frame also contained 3 separate tiffs of the color channels.
The export to TIF as suggested by Alexandre worked, and each file contained a sequence with 3 individual tifs one for each channel.
However, I wanted a color merge of each frame which required the additional step of converting the original sequence to RGB.
Thanks again for a great tool and a very responsive forum.
Best regards