Adding sulfur can help lower the pH of a soil if the lime content is not to high. If there is too much lime the soil is so well buffered that it is diffcult to get the pH to move down and stay there. It may be better to bring in a mix of sand and compost/peatmoss to create a planting bed that is better suited to growing acid loving plants.
If you still wish to investigate the possibilities of lowering soil pH further, the following web site offers more detailed information:
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