I converted them using nero’s command line aac converter and I have no idea if they’re “fast start”
Then they’re probably not optimized for fast start streaming. The Nero codec is one that doesn’t create fast start AAC’s by default. Check out this link for an explanation and options for “fixing” the files:
Look for the FAQ that reads:
When I try to play certain AAC files with iTunes, the SoundBridge appears to “lock up” for several minutes while saying “Preparing to play…”. If left to sit for a couple of minutes, audio will eventually play (or sometimes the SoundBridge will reboot). What is wrong?