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I don't remember that thread. You didn't provide a link, I'm not searching for it since I don't have a problem doing sub domains. If I had seen the thread when it was active I might have commented and helped.
However, the sub domains are not the problem with newbb2 or pical. I've setup many sub domains (xoops and other) and know that it simply works. One server doesn't know about the other and is no different than being on different machines. done right of course.
Can't say what your problem was/is but for sure you can run basic sub domains that don't share any files without issue.