Problem description:
parallel-scp and parallel-ssh are not able to accept
1./ more than one -O options and translate them to -o options of the corresponding applications.
2./ -i (identity) option.
A patch (for parallel-scp) is attached, which solves the issue, though not all possible combination of the optional arguments are implemented and/or tested. A similar workaround is available for the parallel-ssh. Maybe, the argument parsing of the parallel-scp/ssh needs some reconsiderations...
Introducing the use of ':' in the folder description can assign file transfer direction. Of course from remote->local direction the source files shall have different names to avoid overwriting them.
As a wish this could be avoided by the use of hostname folders for the local target...
(This bug was reported https://bugs.launchpad.net/ubuntu/+source/pssh/+bug/387816)