In reply to Lynsety:
I wouldn't think it's worth the effort cycling up Strath Nethy. You "could" cycle the Lairig an Laoigh to the Fords but the easiest way in for a bike will be the long track in from Tomintoul following the river Avon up to the loch. Tomintoul is a long way from Glenmore.
If it was me I'd cycle up to the Cas carpark and walk over the plateau.