Thanks Steven
With a bit of digging in the original C# SVG rendering library documentation, I found that it should support filter effects, but only a very limited range
Filter effects just cut down so much work on the original svg.
Without filters, just adding something simple like a drop shadow, means duplicating the image, adjusting the colour, transparency, position, layer, document size, etc, and doing it all manually.
I'll play around with it some more and see if I can narrow down the list of supported filter effects.