Okay I did a little more research
The enc_aacPlus tool is actually open source command line front end for enc_accplus.dll . See
http://aacpluscli.codeplex.com/
You need enc_accplus.dll, nscrt.dll & libmp4v2.dll from Winamp 5.33/5.34 ( available here
http://www.filehippo.com/download_winamp/2243/ ). You will also need MS Visual C++ 2008 libraries (mfc90,msvcp90,msvcr90) if you don't have it installed.
I can get the command to run in windows and on linux (using wine with winetricks vcrun2008) and it will encode a file into an HE-AAC file. However on linux I don't seem to be able to do any standard input/output redirection which is needed.
In windows when I try and run the commands I can get enc_aacplus.exe to except from standard input but it won't write to standard output. If use '-' as the output it writes a file called '-'! The user Ziller seemed to suggest that it is possible. How did you do it?
Not being able to write to standard output seems to be a reoccurring problems for all AAC encoders when using a Mpeg4 container I've found. I've tried
ffmpeg (using mp4 container)
Nero AAC encoder
faac
and now enc_aacplus.exe . ffmpeg complains that it needs random access to the output file and so cannot use an output stream. I've tricking the others into writing to standard output and they all fail at the end of encoding.
If others are interested in trying this encoder I've zipped up the executable and the needed dll files (the dlls are from Winamp so you won't need to install it yourself). The zip file can be found here
http://www.su-root.eu/temp/enc_accplus_with_dlls.zip