I would first suggest just to try ALAC on the BDP-1, you might not experience the issues I had and with two firmware updates since then it might not even be a problem. I've had enough "chirps" to scare my socks off that I have very little desire to try it.
The easiest method to convert ALAC to AIFF is to have iTunes do it. Change your default import setting to AIFF in the preferences, and then select some files, right click and convert (i.e. create aiff version). I did this by chunks so I could keep track of how many songs were converted, i.e. if i selected 1000 ALAC songs, I better see 1000 AIFF songs, it's easy to sort if you have the right columns listed in iTunes.
Once I was happy that the "chunk" of files properly converted I removed the ALAC files from the database, but I actually left the files, which I archived to another USB HDD as a long term backup.
With this approach you will keep all your embedded tags and also any information that the iTunes database itself keeps (i.e. album art). Works fine for both Windows and Mac.
For a Mac, MAX is another option to mass convert, and I've used that before to create FLAC and compressed versions of the ALAC/AIFF files. You won't lose any tags that are actually stored in the file, but iTunes handles the artwork differently for albums. If you want to also keep your album art, you will need to copy the artwork and then save it to all files in the album (there's another post with detail steps). All the apps for Mac will use the coreaudio library when converting to ALAC to AIFF, so iTunes or Max will do the trick.
For MAX, to convert to FLAC is rather simple, if you have a dual core set it to run parallel 3 jobs, four cores set it to run parallel 5..
To convert ALAC to FLAC on Windows, others will have to provide recommendations.
