There are no direct buses from any park or DTD to the MK. Only from the Disney resorts, it's one of the perks to stay at a Disney resort that you generally bypass the TTC, while day guests coming from other parks have to take the monorail from TTC to MK. There are however buses between DHS and DAK and from Epcot to DAK, to DHS from Epcot you have to take the boat launch via International Gateway.
There is also a bus from DHS to Epcot--the boat leaves you at International Gateway, and the bus takes you to the front of Epcot, which is handy if you want to get directly to Future World.