Sailnut, unfortunately you are exactly right.
I somehow talked my girlfriend into letting me see the regulator before Christmas.
It was very difficult to screw the Fluval cartridge in, even before getting close to puncturing the canister.
It was impossible to get the Walmart canister in past about 1.5 - 2 turns..
With that said, the adapters we have all been talking about will definitely not work, at least not in theory.
I think my plan at this point it to return the Fluval kit, despite the great reviews people have been giving it.
I think I am going to go with a regulator regulator/solenoid setup, possibly from ebay. I have been researching the Aquatek regulator/Solenoid. It seems to get good reviews and is very reasonably priced. Because I plan to use this on the Fluval Ebi, I will get a CGA 320 - paintball tank adapter and use either a 20 or 24oz paintball canister because I don't have the space for a 5 pound canister where my Ebi will be going.
I am kind of disappointed, I really like the Fluval kit. But when comparing the cost of replacing the 88g canisters, most likely once a month if not more due to having to run it 24 hrs/day, I will break even in just a few months when spending the extra $75-$100 (maybe even less) on a different set up. I would then also have the option of running multiple planted tanks off of 1 regulator in the future should I get more tanks, and I probably will lol
I do hope someone comes up with a solution for this at some point, I am sure there will be many happy users out there if someone works it out!
Sorry to be the bearer of bad news!!
Hope everyone has a great holiday!