What player are you using to play back the Speex files? Max uses the unstable branch of speex (currently 1.1 but soon to be upgraded to 1.2) so perhaps the player isn't correctly handling the 1.1 generated files?
What format are the files you are attempting to convert? I've had problems in the past with sample rate conversion and Speex, but I thought I worked those issues out.
BTW, even if Speex in the current release of Max is broken, you can still use the command-line encoder on Mac OS and thus avoid resorting to Windows!
I got the quicktime components for Speex and played them in Quicktime as well as in VLC. Speex files provided by my client played fine in Quicktime, and with some cutting off of audio in VLC. The Max files played garbled noise mostly