Thanks SCM for the information and the links. I know that canned is much better for him than dry especially when urinary crystals are a problem. The problem is we tried that when he first showed signs of crystals. All cats were changed to wet food only. At the time it was a very expensive undertaking but I did it. The problem came when it did nothing for his crystals and he became sicker with wet food only and almost died from one bout. (he had been on wet food only for 3 months with blood in his urine constantly when he had the severe bout)
At that time the reason I had switched to canned for all of them all the time was he wouldn't touch any of the prescription food, wet or dry so we went to a high quality wet. (it's at least 5 years ago and I don't remember which one). When he almost died and needed hospitalization for several days to clear him, we tried the prescription food again and this time he ate the dry but would have nothing to do with the wet. So I put the others back on a mixture of dry and wet and they were happier with that because they could eat whenever they wanted with the wet given twice a day until they were full.
I then agreed to try him on the prescription dry because he would eat it and was fine for several years until I introduced the high quality regular wet food again and he started having occasional bouts of crystals with blood in his urine and needing medication to clear his urinary tract.
So we are now at the point where I want to give him a diet totally made up of wet food but I wanted to know a dry food for the transition period that would be somewhat equivalent to the Royal Canin SO. I also have to find a wet food that doesn't cause an increase in his bouts of crystals as the one I'm using... Merrick... is not keeping him totally clear. He has been eating dry food for the better part of his life and the SO has definitely made a difference in his urinary tract disease. He also does not adjust well to new foods including refusing to eat and crying all day for food. I know he can stand to go without food as he is fat but he takes it into several days without food and that is also not healthy for him. I have tried giving him fish straight out of the can and he doesn't like the taste of it.
So again I ask is there a high quality dry food that might be somewhat comparable to his Royal Canin SO and a high quality wet food that is also recommended for cats with urinary crystals. I can find several in a google search but I wanted to know if anyone has experience with them.