Photos not synching from iMac to new iPhone (or prior iPad)

I've spent the last 2 nights searching the web for answers, but no luck. It appears something is out of sync since my cutover from iPhoto to Photos earlier in the year. Specifically:

1. Purchased new iPhone 6s, restored from prior phone load (iPhone 6), and had no photos. Upon opening Photos on my Mac, clicking Synch All Photos & Albums, I receive an error of "iTunes cannot sync photos to the iPhone because your Photos Library is not yet available. Please try again later."

2. Upon trying to troubleshoot, I looked at my iPad, which I previously had synced a few select albums to, and noticed that the "Synch Photos" box was unchecked. I confirmed my iPad still had the previously synched albums and re-checked the box. Upon synching, I receive similar error to above.

I do not want to sync all my photos (several hundred gig) with iCloud Photo Library.

Other settings on iPad & iPhone are:

iCould Photo Library = off

My Photo Stream = on

iCloud Photo Sharing = on

I also verified with Option-click on Photo app that my Photos Library is the Systems Photo Library.

Thanks in advance for your help!!