From Scholastic's interview with KA Applegate (For reference; I know it's been mentioned)
Q: "How do you pronounce the following names: Hork-Bajir, Visser, Tobias, Elfangor-Sirinial-Shamtul, Ket Halpek, Andalite?"
A: "Here's how I pronounce them: Hork rhymes with "cork," and Bajir sounds like "buh-JEER"; Visser rhymes with "kisser"; Toe-BYE-us. Oh, good grief, you asked me a tough one. Okay, it's "ELF-un-gore Sir-RIN-ee-ul Sham-TOOL; Ket Hal-PEK; and finally, AN-duh-lite."
I used to think "Hork Badger" when reading the series too, but I think I'd managed to switch to the correct pronunciation in my mind by the end. Tobias is a name, with real-world precedent for the pronunciation, and one I haven't read incorrectly since I knew a real Tobias (was at my school for all of like two weeks) Haha... Arrested Development never fails to remind me of Animorphs. Oh Tobias...
It definitely feels more correct to me to say "visser" with a z sound. I always put the emphasis on the second i sound in Aximili: ax-uh-MEE-lee. For some reason, I always want to roll the r's in "Esgarrouth;" EZ-ga-rrrrowth (soft th). Makes saying Ax's full name more fun