I erased the hard drive on my MacBookPro7,1, and installed a clean copy of High Sierra. Then, I opened Migration Assistant, and tried to move the data from a sparsebundle on my MacPro3,1 to the laptop. There appears to be no easy way to do this anymore. From what I can tell, Migration Assistant only allows moving data from complete startup drives, and no longer recognizes mounted disk images. Does this mean that my only hope for migrating the data is to clone the mounted sparsebundle to become a startup disk on an external hard drive (over FireWire, since those are the enclosures I have)?

Or, more broadly: Does anyone know the right way to migrate data on a sparsebundle on my tower, to the startup disk of my laptop?