If both machines are in the same Network, you could also use one machine as "the master" with a folder where you store all your BIAB-Songs and allow access on your lokal Network for your second machine to this folder.

I personaly have a NAS-Storage with 2 disks in raid 1 - mode. This way i'm save in case a disk fails as it writes everything on both disks. All my user data like song-files from BIAB are stored on the NAS-System.

If you two machines are not in the same Network, than a cloud-storage like dropbox or OneDrive as Matt mentioned is a good solution.