Ive tried softs from many W and K on my k800, and currently, the 'most compatible' is from K770, only few problems with joy, and saving photos. All other keys works fine, it is stable and nice.
There is no Walkman, but flash menu would be enough for me...
But k790 is not 3G, and that might be problem, i think you cant put flash from 3G into EDGE, and EDGE into 3G also dont work(ive tested k800@k790, not working)
So there is only way - wait for crossflashing or 'walkman' or 'flashmenu' patch for k790/k800 :P