nevermind. I'm an idiot. I had it connected to my node, which happens to be down atm, so it wasn't even scanning for transactions properly. Everything works now. Thanks for your help!

Yes, I do. I'm not sure how to find the master fingerprint within Samourai, but I've tried both with and without my passphrase, and it's still showing no coins and no history. Coins are still in Samourai, postmix wallet.