Thanks. but i want to be able to change at runtime - eg have a playmaker varible (float) which i can feed into the start command. Eg if i want to scrub forward (mainly whilst playtesting) i can drag a start time bar, forward to the specific section (sampletime) of the track i want to start at - and resume.
I'm afraid that's not functionality we have, with or without Playmaker. I have no issue adding Playmaker actions for stuff that exists in core Master Audio. You can probably change the property (start time) of the song using some stock Playmaker actions that have nothing to do with Master Audio, prior to telling the song to play. But I'm not a Playmaker expert, so I can't walk you through that.
Do you want me to check if there's a "seek to time" functionality after playing? Playmaker may be able to natively call that as well.
No need to pause or unpause. You should be able to seek.
Basically you need to grab the ActiveAudioSource property of the PlaylistController and set it's "time" to whatever you like. As I said Playmaker should have default actions that use Reflection to allow you to do this, but I haven't used them.