i am going to assume you are using Formula One or FormulaTwo. i have had the same experience with the "rubbery-ness" of that food. i really didnt experiment too much with cutting it frozen or cutting it thawed, but i would expect the same results either way.
since then, i have changed to san francisco bay frozen foods... mainly because that is what the LFS
had in stock when i got mad at the Formula food. The SF bay foods thaw down really well into small / tiny pieces. everything in my tank is able and willing to accept this food when i feed.
i have also had good luck with the Spectrum flake and pellet food and the Formula flake food. So, you may have to try a few different foods until you find what your fish like. i mainly feed frozen now, and i mix equal parts brine w/ spirulina, marine cuisine, and emerald entree (all by San Francisco Bay). that mixture gives me a nice blend of foods for the various creatures in the tank. i feed 1 cubes worth of food, 3 times a week...
selcon will help some finiky eaters, but you should try to have something that they already are willing to take...