Hi Sherri and welcome. I'm around your neck of the woods (I'm in London). I actually feed Fancy Feast low carb varieties - mostly the Turkey & Giblets classic pate because it's the lowest phosphorous - Genghis doesn't have urinary or kidney issues but I guess I'd like to avoid the high phosphorous if I can. I do also feed the Chicken Feast and Tender Liver and Chicken Feast, as well as some of the fish varieties on occasion. I always water down her food with a few tablespoons of hot water - she prefers the warmer temperature and licks the plate clean. When I would just smush it up, she used to leave a lot behind.
I did try the Nature's Variety Instinct Chicken but Genghis doesn't like it (I think it smells WAY better than the FF, but what do I know?) If you find it a good food for Shamus, be sure to buy it in the dog section in the big 13 oz cans. Much more economical and it's identical to the cat one in the smaller cans. I actually feed my crunch-junkie Picasso the Instinct dry variety because it's 17% carbs - about the lowest I'm able to find available in my area - until I can get him converted.
Interesting about the PC food - the Nutrition First line looks to be the lowest carb - I ran the guaranteed analysis of the chicken, tuna, sardines, kelp variety through a carb calculator and got this:
My only hesitation on this food as a daily feed is the tuna and sardines - like Asreal, I don't feed fish regularly and I'm not sure where they are sourced so mercury intake may be an issue. I would have no issue feeding it on an occasional basis for sure.
I also ran the "regular" Extra Meaty line both chicken and turkey & giblets through the calculator and got a good low number on wet matter, but a little high on a dry matter basis at 13%. The chicken and liver one comes in at 9% DMB.
If Shamus likes pork, Hound & Gatos makes a pork food for cats that seems to come in pretty low in carbs but they don't post the ash content so I can't be 100% sure, and it's also pretty high in fat and calories. I can usually find it in Global Pet Foods.
I'm like Wendy - I have the catinfo.org chart on my phone so I can remind myself when I'm in the store and might see something on sale I can try. The Weruva foods are so lovely and smell divine - they are excellent quality but Genghis won't eat them

. I've considered mixing a mid-carb smelly food with Almo or Tiki Cat 0% carb varieties - anyone else ever done this?
Good luck with Shamus and your food adventure!