The answer is strong maybe. If the system supports SIP 2.0 and you are speaking of the 3CXPhone6 softphone application and not the 3CXPhoneforWIndows12 which is only usable with the 3CX platform, then you can likely use it. However, the 3CXPhone6 application does not support all the features that your PBX may provide such as presence. There may be others as well.
As the software is a free download, you could always try it and see.