Visio figures can be easily converted to EPS format by following steps.
1. save the visio figure in PDF format. (Before storing in PDF format, goto design tab at the top, select size and then select fit to drawing from drop down list).
2. Open the PDF image in inkscape (can be downloaded from: https://inkscape.org/release ).
3. select poppler/cairo import in inkscape when asked.
4. Finally save figure as an .EPS format. (Final window will appear asking for desired DPI)
5. Done (See the attach figures for better understandings)