Answer: Unfortunately, it is often very difficult to plant beneath maples because they have very aggressive root systems which steal moisture and nutrients from the soil in addition to the canopy preventing rain and sun from reaching the neighboring plants. So I want to caution you that it may not be easy to grow a successful replacement; it may be that your better choice is to keep the burning bush even if it does not color well in the fall or is growing a bit thin due to the excessive shade.
The only shrub I can think of that might grow there and meets your criteria is Hydrangea arborescens. It will need special attention to watering. There is a photo and description of a cultivar named Annabelle at the following web page. You may need to cut and paste the complete url into your browser to make it work correctly.
Another option might be to use a large and impressive, attractive urn or planter and fill it with colorful annuals such as impatiens each summer.
Your local county extension and local professionally trained and certified nurseryman may have additional or different suggestions based on a more detailed understanding of your growing conditions and design goals. Good luck with your project!
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