Well good luck in your search. Just consider the following things when sourcing your cat food.
Best to look for the higher real meat /fish content (not just protein content),
Best to avoid products with wheat in.
IMO best to avoid soya altogether particularly GM (I have seen cats ignoring certain chunks when eating certain cheaper brands of wet food and always assumed those could be lumps of soya protein :/)
Intorduce the new dry food slowly if possible, adding a little to what they are used to and gradually decreasing the ratio of old food to new - over a week or ten days is recommended but at the very least try and do it for 3-4 days to get them used to it.
And do consider giving them wet food (or raw, but that's another thread) for at least one meal a day (separately from biscuits) have you tried the little hi life tins or feline fayre? I'd like to see a cat turn that down - little bits of calamari in tuna and real chunks of fish in jelly - and not a soya bean in sight

xxx