We did it again - because it is indeed a nice trip: hiking from Elm over the Segnapass down to the Vorderrhein and then packraft until the Hinterrhein meets the Vorderrhein and finally becomes the Rhein River as we know it. Be aware that the Martinsloch is part of the UNESCO world heritage.
The hiking part can be found here - not too complicated, except for a little snow field right under the mountain lodge for which we had the wrong shoes on.
The Vorderrhein had around 40 m³ / sec in regards to the speed which was nice and relatively easy to handle. According to these folks this river part is rated as II/III - but could be different due to the low water level we had.