I'm waiting for a vet update as I write this. He definitely still seems blocked, we tried the Albon tablets for 4 days and nothing has really changed besides his behavior- he's not going in & out of the box multiple times anymore. But when he does use it, he goes in for quite a long time & it seems like he only manages to get out a little bit of urine. He still seems healthy and happy though! I'll post more when I hear what happened at the vet.

Thanks again for all the positive thoughts and prayers- our cats are our kids and I can't imagine what we'd do if this turns into something really serious...