I think a tram link from Stockport into Dibsbury may be needed first, then a Marple link to Stockport as an extension of the train/tram.
Even then it will not be quick to get to the airport, or MediaCity. Not many people work near Stockport station, so a link that just goes to Stockport does not help much with commuting.
We are hitting the old issue that where employment and housing is on the edges of a city and public transport links into the city, the car is very hard to beat! (I keep coming back to failing to understand why people in Marple wish to travel to Stockport….)
The A6-Bredbury relief road is a separate issue and may allow bus lanes to be installed on more of the A6, if so, we just need a way for a bus to get from Marple to the A6 in a reasonable and predictable time.
The only way to remove congestion is to have road charging, as whenever a car is removed from a road, travel times speed up, so people start working further from where they live.