As addition to the Ambisonics Decoder, Microphone Processor and LADSPA Plug-Ins I compiled and packed the convolution software jconvolver 0.9.2 as easy-to-use installer for Mac OS X >=10.6.
This Jack client is a very flexible real-time convolution engine, including configurations for applying Multichannel Ambisonics reverb.
You can find some additional Ambisonic reverb impulse responses here:
The Jack Reverb Plug-In with Ambisonics mode zita-rev-1-0.2.1 is available here:
All developements by Fons Adriaensen:
Get more information about Ambisonics and Ardour in an article by Jörn Nettingsmeier.