Taking the bus to MK is pretty much your best, and possibly only, bet given the time in the morning - Disney Springs busses won't be running generally until 11am to the resorts, so you can't use that as a hub. You can pick any of the parks, which depending on your ADR time you'd be best to pick parks with earlier openings. MK is the most convenient, because it gives you a few options to get to Poly - the monorail OR the boat. The boat will stop at Grand Floridian, then Poly...the Monorail will stop at Contemporary, TTC, then Poly. If the boat is at the dock or approaching, that will likely be your faster option - if it just left as you get there, the monorail will probably be faster.
If you use any other park as your transfer - you'd be taking your bus from Pop to that resort, then transferring to the Poly bus.