To follow up, I said yes to the second question (about exceeding duty free limits), got an X, and declared the alcohol to the officer. No duty was charged and it added all of 90 seconds to the process.

As an aside, DTW immigration was great. It's much nicer than ATL, JFK, SJU, and others I've been through. They even had a dedicated customs line for GE, something I haven't seen before. When I was waiting for my bags, the ag beagle came up and poked his nose into my wife's bag. I told the handler that there was candy in the bag and she said "If that's candy then we have a problem". I told her I declared it and she replied "No, not you and me, me and the dog!"