After trying a bunch of different higher-end brands, and using Kirkland Lamb & Rice and Nature's Domain from Costco, I finally broke down and bought Pedigree from Costco yesterday (after pulling my cart over to check GreyTalk and make sure that I'm not a horrible person for buying the big yellow bag, ). Aston seems to do okay on foods for awhile, but then starts to get squish-poops no matter what. We have had him on ProZyme all along as well (it is BAD NEWS in terms of gas if we don't). On top of this, I would really like him to gain a few pounds, but if we try feeding more than usual of any of the above foods, it goes right through the poor guy in terms of poop volume and squish. AND, the higher-end foods seem to be more concentrated, so we feed a lot less to keep his weight up in general, but Aston is left wanting (noticed this on INNOVA especially). I've tried bulking up his food with green beans, etc., but with the other factors, I figured it was time to just buy a cheaper, bulkier food and see how it goes.
His poop today was squishy as usual, but we also don't have the feeding quantity worked out yet (we're going about half Nature's Domain, half Pedigree -- probably as an ongoing thing, unless the Pedigree itself seems to be working better on its own).