Benoit, there are no OpenSSL equivalent commands do batch decrypt files in AxCrypt.
AxCrypt 1.7 had a command line interface but AxCrypt 2 doesn’t as of yet. You could suggest this to AxCrypt although I don’t know how popular such a request is and thus how feasible it would be for them to provide it.
You could create a Windows virtual machine from your Mac because that’d allow you to decrypt your files – although not in bulk.
The other option is to use something open source and cross platform like GPG Tools on Mac and Gpg4win for Windows. That wouldn’t allow you to decrypt AxCrypt files bit it would allow you to share between Mac, Windows PC, Windows Phone, iOS, Android, Blackberry and Linux.