I suppose in Haali splitter MP4 support is enabled.
AAC sound could be handled by
either ffdshow filter (find it
here)
or by
CoreAAC.
If you perhaps already have ffdshow installed maybe verify that "AAC / libfaad2" is also listed under "Codecs" of "ffdshow audio" (and that it isn't disabled there).
But maybe first give BS.Player's codecmanager a try.
You can find codecmanager.exe in BS.Player's installation folder.
Did you already find and read BS.Player's
wiki/faq concerning sound?