I actually just had a go at converting the RJS Guitar instrument on Pianobook for Tonverk. I ran the Decent Sampler version through Convert With Moss, then used the elmconv - EXS24/SFZ to .elmulti Converter.
On first glance it turned out OK - it worked, it has velocity layers and sounds decent, especially through Dirtshaper. The resulting multisample was ~290MB so I want to have another pass to thin it out, but other than that it seems promising for a nice, clean guitar sound for Tonverk.