Did you happen to find a solution to this problem? I've just run into this myself.
irritating.. I have 12 solaris 11 hosts out of the 1200 servers my script needs to run against. I'm leaning towards just moving these 12 to linux because they are headaches in a dozen other ways as well when it comes to system automation, etc...
unfortunately I didn't find any workaround, Solaris SSH is an old fork of openssh and dose not support the multithreading option. I cant comment on your Solaris 11 > Linux environment, most of our environment's where migrated from 10 to 11.1, and all I can say is Solaris rocks, features you find in Solaris you can find on any other OS in the market just to name a few ZFS, BE, IPS, FMA, SMF, etc..