From the website:
Pianoteq 6: a mature technology
Pianoteq 6 brings numerous refinements in its engine and physical model, increasing realism and acoustic presence on all its instruments: acoustic pianos, electro-acoustic pianos, historical instruments and chromatic percussion. Pianoteq becomes, more than ever, an immense joy to play.
Authorized by Steinway & Sons
Steinway & Sons have approved the sound and playability of the Pianoteq virtual instruments Steinway Model D and Steinway Model B, which have gained from the refined physical model. These magnificent virtual grand pianos will appeal to all musicians in search of the most famous piano sound signature.
Increased compatibility and extra features
Pianoteq 6 facilitates your workflow by adding compatibility with the VST3 format and the ARM architecture (Linux version only, for example on Raspberry Pi 3 boards). It includes chord identification, and the tuning section has become even more advanced with new tools. The standalone version now offers a MIDI playlist, an improved MIDI archive, and the ability to export audio to FLAC and MP3 formats, in addition to WAV