Why do you need slides? And how many, how often - do you need an automated solution at all? Do you really need the ppt format?

If you need large numbers of graphs routinely updated and circulated wouldn't excel more or less on it's own (once you have pulled in the data) be a much easier and faster solution?

And can you not do what you need with VBA?

VBA will probably do the trick. I've used it to generate PDFs (through Word) from Excel sheet data + external image sources so you can probably do the same with PowerPoint.
(those third-party toolkits must be using VBA 'under the hood', anyway)

Thanks, I will look into VBA more thoroughly. I have some basic knowledge of VBA, it's time to dig deeper.
Jack