Maintaining a link to Develop/ACR edits in a multi-layer Ps document

You'll need to do the extra adjustments in PS by double clicking the smart object layers and launching ACR. What is happening here is that each smart object is actually a copy of the raw file, so those edits don't get sent back to Lr.

However, have you ever tried using linked smart objects? With this new-ish method, your smart object layers are actually links to external files - which may be the original raw files. So you could then edit those raw files in Lightroom, save the xmp, open the PS document and update the links.

Ah, the linked smart objects is what I was looking for. I had assumed that since I had xmp's chosen in my ACR prefs that it would happen automatically but as you said the the objects are new copies of the raw file. Thanks!

For future readers...

you can create a linked smart object from the Layers Menu in Ps.
Layer Menu > Smart Objects > Relink to file, then carefully choose the correct image in the dialog box.
I did have to Synchronize the folder when I came back to Lr to get the new xmp info to update visually.

If you only want to update one or a few images, you don't have to synchronize the whole folder. You can select the photos in Lightroom and use either Save Metadata to File (to push Lightroom edits out to XMP for ACR to pick up) or Read Metadata from File (to pull ACR edits back into Lightroom).

Those commands are under the Metadata menu in the Library module, or under the Photo menu in the Develop module.

Good point. Would save time for a folder with many images. I don't see a slow down on my typical folders, with 200 images or less. Is there another reason to worry about using one or the other method?

Not really. I would use Save Metadata (Cmd S), because that is all you actually need to do. Synchronize can invoke importing or removing missing files too, which you might not really want. In either case, saving metadata happens in the background.

My candidate for the most interesting new tidbit to find out about in quite a while, thanks for pointing out that smart/link feature.