It seems that your problem lies with the amount of water.If you need the 1 kilo of water if you use rusk you will need 600 plus gms of rusk.
I have had a simlar problem with making beer sausageswher I needed 20% liquid and in the end I used soy protien at 1 to 5 thats 200gms for your 1 kilo of water.
This resulted in a very firm and succulent sausage which was not 100% what I was looking for but nevertheless an improvement on my attempt with rusk.
Next time I may try a mixture of rusk and soy.
Texture is really a matter of experimentaion and personal preference.
Sorry cant help with the milk powder as Ive never used it.
Jim