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Rav Schwab on Prayer (compiled from taped lectures under the editorship of his eldest son Rav Moses L. Schwab) Iyun Tefilla, Hebrew version of "Rav Schwab on Prayer" Rabbi Shimon Schwab was officially "retired," but his mind and conscience never rested. Always a great thinker and teacher, he turned his attention to the Siddur.
As for me, My Prayer by Rabbi Dr. Nissan Mindel is such a book. It doesn't have quite the academic bent that your question implies, but it does give the history of the prayers and why they are placed where they are. It does not much touch on the variety of customs in different communities.
Artscroll interlinear Tehillim will cover most of it either in a short preface to each chapter or in the notes on bottom.
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