At the moment, I am using mathspec and some traditional math packages such as mathpazo to typeset my mathematics. The results are mostly satisfactory, but I would like to expand the repertoire of some of the math alphabets by replacing the traditional packages with fragments of Unicode math fonts; in particular I want to be able to use the blackboard bold letters and numbers from STIX for \mathbb.
Now, the problem with using the unicode-math package is that it is totally incompatible with traditional math packages: it insists on replacing all the existing math symbol macros with Unicode ones even when no Unicode math font has been selected yet. I am not yet prepared to switch over to Unicode math as my main mathematics typesetting system, as it is very hard to get it to reproduce my current output. Yet, unicode-math seems to be the only way of using fragments of Unicode math fonts in the way that I want; the \setmathxxx commands from mathspec expect old-style fonts with the styled glyphs in the Basic Latin block.
unicode-mathpackage, not the Unicode character output font)texdoc luatexis terse and assumes understanding of how the non-Unicode primitives work (documented in TeXbook).