First, welcome to FlyerTalk, Jeff.

Second, have you verified that the Flying Blue website knows about award flights from JAX at all? (Delta's website does not know anything about KLM CItyhopper flights on either a paid search or an award search; the onlyl time they find them is on paid connections to flights from the US to AMS. Well, if Delta can be blind to KLM's "smaller" intra-Europe flights, Flying Blue might be blind to Delta's "smaller" intra-USA flights.)

So check availblity on Delta's website (Detla being Flying Blue's partner in the US) for your connection to DTW alone. I don't know what the maximum connection time is on Flying Blue, but another possible issue is that sometimes a website won't show a connection that's beyond a certain connection time, even though it's still at "legal" connection time.

So it might be useful to know if there are any flights JAX-DTW (or elsewhere bearably near you to DTW) that day or the day before on the way there, and that day or the next day on the way back. If there are, Flying Blue might be able to put them all together as one award on the phone, even though the website won't.

Third, you might want to consider whether you'd be open to driving to (and parking at) the next airport over, for example MCO (Orlando) which is about 2.5 hours drive from JAX, and then search for MCO-DTW availability. MCO being a much bigger airport, it's possible there might availability from there while not from JAX. (You could also check Savannah, which is less than 2 hours drive away, but it's no bigger an airport I bet, so I don't know how more likely it is to have/show avaiability.)