I went first time last weekend, so not really local knowledge.
This is a rough version of what I rode last week but not going to the Res (maybe simillar to the GMBC route you did). Knock of Crief anti-clockwise, when you get to Kate McNeivens Craig there’s a track off to N, go through deer gate and drop onto contouring path. At the end climb up to summit view point. Drop down to car park and then head N through ford at Hosh. Head W past Loch Monzievaird on the N bank. Go out to A85, cross onto track leading to Thornhill Lodge, first L (head E) past small pond, take first right (S) at end of wood (100-200m on)drop onto trowan-laggan-crief track parallel to river and railway. Head W to Trowan, climb to monument if want. Head back on track from Thornhill Lodge over hill to Crief. Joining your outward route for a bit.
SMBO routegadget site has the map from last weeks SMBO whic shows some more tracks than the OS