After much to-ing and fro-ing with visas and seasons, we're pretty sure we've now got a route, and here it is!

 trans-siberian out, silk roads back

Exciting and scary!  After an initial detour to Toulouse we shall head up through North-East Europe to St. Petersburg and take the trans-Siberian to Mongolia and on to China.  After some frolicking in South-East Asia we're off back home along the Silk Roads.  So basically, follow the map clockwise!