I hope David Reigle does not take this the wrong way but intrigued by his reference to Shankaras criticism of Buddhism in the commentaries on the Brahma Sutras I find the reasoning there less than persuasive, which leads me to believe that the author is not the original Shankara. As further evidence: Subba Rows persuasive arguments in SRI SHANKARACHARYA'S DATEAND DOCTRINE. Here he argues that the evidence from the traditional mathams point to Shankaras date being much earlier than the Brahma sutra commentaries could have been ( circa 500BC according to the "Tibetan and Indian Initiates.")
The Madhyamika and Yogachara philosophies criticized in the Brahma Sutras are of a much later date (and even the philosophy of 'momentariness' is of doubtful heritage). Also the idealist philosophy criticized there has been and still is a persistent strand in the Vedantic philosophical tradition.