Mike, and vwinter, thanks for your input.
I'm now cautiously optimistic that I won't have a problem, because when I'm listening in my quality time, my damned phone will be switched OFF! Really looking forward to getting this micro-rig up and running. I will do a quick test when I receive the 2Stepdance from Jan some time next week and report back. If I think there's an issue then another 110 Euros will be in order, but hopefully not.
I am an avid concert taper and already use an M10 - awesome machine. Using an M10 for playback seems a natural progression and I have read many good things about the line-out performance here on Head-Fi. I've never used an iPhone or iPod and have no desire to do so.
I'm now planning to get a second M10 for heavy duty, long-term every-day listening, just to keep my M10 recorder in pristine nick for those critical gigs!.