Bi-Directional Music On Hold
Can you clarify what you mean by bi directional? Most music on hold players have a single RCA output, intended to plug into a music on hold port on a pbx phone system. Those music on hold players output audio only.
On hold players like the OHP 6500 you mention essentially patch the audio into your phone lines while a call is holding. The 6500 uses the existing hold button on most standard (non-pbx) phones, in conjunction with a little dongle that connects to the curly handset cord.
If you're just trying to record content from a phone call, you can do that with either a call recording service, or you can physically connect a phone patch device (like the TR-70) and run the audio jack to the mic input of your Mac. Hope that helps, but if I missed the mark on what you're trying to do, just let me know.