Not really sure why there aren't any kings that return to POW is. rivers, the rivers are small by our standards with the largest (the Thorne river) not quite as big as the Kalama, I would think they could do okay in that system and a few others but I can't explain why none are present.
As for silvers, don't expect 20 pounders, in 15 years up there I've got a grand total of 0 that size, you can catch 10 to 15 pounders all day long but very few over that size. Last season with 20 to 22 boats a day on the water, usually fishing 4 people and most boats bringing in silver limits daily in July and August, I can think of 5 silvers that were over 15lbs. 1 of my guest brought in an 18 pounder that was the seasons largest, better stick with the Satsop or OP rivers for the big boys.