Glad you got it working. Even happier that that command line works!
That use to have quite a few issues with spawning a infinite xboard apps...
Sorry to hijack your thread, but since both mac xboard users are here, I thought I'd ask anyway.
I have a bit of a problem that I wondering if it was a larger problem.
The way XBoard.app is suppose to work is it is suppose to be able to switch the icon on the dock to white and black versions of the knight depending on whose turn it is. (or the red and black Ma for the Xiangqi version) Also if you open the "Engine Output" window under the "View" menu, you are suppose to see dots indicating which engine is white, which is black, and which is unloaded with a grey dot. Also in the same window you are suppose to see if the engine is thinking/pondering, or waiting with another couple of icons. This is all due to the magic of gdk pixbufs.
Now on my laptop, which was my primary dev machine, this all worked fine. But when I tried it on a school computer, I noticed it didn't work. I originally thought this was due to some permission issue. Without having admin access to get past gatekeeper, I was launching stuff via the terminal. So permissions didn't seem out of the question. But then I built myself a 'hackentosh'. Now it has the same problem. (Which could be explained by the fact I'm using a hacked kernel which has other icon problems) But it has me really worried. Did this pixbuf feature ever work on either of your machines?