Hi there, I’m aware that this particular topic is ‘stale’, but I just wanted to say that the latest versions of phpBB actually work quite well with Manticore. The main problem is fixing permissions (as the old saying goes, ‘90% of all Unix issues are permissions’), and a few of the directives are marked as deprecated by Manticore (e.g. replacing read_timeout with network_timeout), but, in general, it works quite well.
Here is a discussion related to relatively recent changes to the native phpBB implementation of Sphinx Search, where they also discuss the obsolescence of Sphinx and propose a change to Manticore Search instead: Future support for Sphinx Search - Page 2 - Development Discussion Board
Here is also a reasonably current, detailed configuration page for Sphinx under phpBB (most of which also applies to Manticore): phpBB • Free and Open Source Forum Software
In other words, it seems to me that, a year after this thread has been opened here, Manticore can be safely used as a drop-in replacement for Sphinx — and, indeed, I certainly manage to get phpBB3 to work with Manticore without issues.