Rattlechains + Panharmonicon should be a great combo. I tried it with two 6-cost spirits and they failed to get the 6-mana boost from Rattlechains some of the time. I think the Rattlechains boost doesn’t trigger when a spirit is drawn via Panharmonicon.
Rattlechains works only on cards that have been drawn or effects that says ‘Draw’, It does not apply to cards that have been ‘Fetched’