The version suffix, .6, you mention is the "SO version" of the libimobiledevice shared library. It is defined in line 18 of configure.ac
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You can find out when the SO version was last changed by running Git Blame on configure.ac
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The version suffix was last changed over six years ago. So any version of libimobiledevice from the last 6 years will do.
You're best off using the latest released version (1.3.0, see https://libimobiledevice.org/#downloads) or just the latest version from Git. libimobiledevice is very backwards-compatible and I can't think of any reason to use an old verison of libimobiledevice.
If the file name you get after building libimobiledevice doesn't match the file name you're looking for, you can just rename the .dylib.