Bhikkhu Analayo's book is investigative, and has a tremendous depth and breadth exhibiting a great deal of sutta knowledge. It isn't practical in the nuts-and-bolts "Mindfulness/Beyond Mindfulness in Plain English" sense, though. I found it very insightful in regards to Satipatthana, but I wouldn't necessarily call it practical. Nanananda's Nibanna Sermons are a little more focused (perhaps it would be fair to say it is because he is asserting meaning more-so than Analayo), but the practical bits are more in terms of clarification than instruction. I still find him somewhat vague in a specific practical sense. I would recommend reading both, but they may not suit your need at the moment. Could you give a little more info about what you are particularly interested in investigating regarding the Dhamma? Practical in terms of meditation?
I am currently reading "The Island: An Anthology of the Buddha’s Teachings on Nibbāna" http://www.abhayagiri.org/main/book/1788/
(thanks to a suggestion by mikenz66). It has a good amount of depth and breadth (quoting from various sources & suttas). It seems to have picked up especially in and after the chapter Atammayata: “Not Made of That”
There seems to be some practical use in terms of clarification, but I am only about half way through it.