If I understand well, there is no complete solution to my problem, yet. I should wait until this will be fixed into Mathspec, shouldn't I?
Maybe, there is a complete solutin (at least as complete als Linux Libertine lets it be). In order to determine that, you should give a detailed specification of what you _want_. Until now, you mostly said, what you _did_ and what problems occured that way.
If all you want is the support of unicode math alphabets including bold greek letters (u1d6a8 to u1d6e1), then the unicode-math package with a math font supporting these glyphs (like Asana Math) seems to be a near complete solution.
If you want additional siunitx support (for bold greek?) within xelatex, it get's a little bit complicated, as siunitx's detection algorithm seem to not really work together with unicode-math. Using the keys mode and math-rm / text-rm (and associeates) together with the \fontspec or \mathbf etc. can most probably get you, what you want, albeit being ugly code.
When the exact problems are cleared, one might file a bug report / feature request to the siunitx maintainer Joseph Wright. (Maybe he is even reading this list.)
Math alphabets in Linux Libertine O might come with Open Math support for Linux Libertine O.
Attached you find a small analysis of trying to get bold numbers in Linux Libertine by siunitx.
bye Toscho
\documentclass{minimal}
\usepackage{fontspec}
\usepackage[bold-style=ISO]{unicode-math}
\setmainfont[Color=0000FFFF]{Linux Libertine O}
\setmathfont[Color=FF0000FF]{Asana Math}
\setmathfont[Color=00FF00FF,range="0030-"0039]{Linux Libertine O}
\setmathfont[Color=00FF00FF,range="1D7CE-"1D7D7]{Linux Libertine O}
\setmathfont[Color=00FF00FF,range=\mathbf]{Linux Libertine O}
\usepackage{siunitx}
\usepackage{booktabs}
\begin{document}
\begin{verbatim}
\documentclass{minimal}
\usepackage{fontspec}
\usepackage[bold-style=ISO]{unicode-math}
\setmainfont[Color=0000FFFF]{Linux Libertine O}
\setmathfont[Color=FF0000FF]{Asana Math}
\setmathfont[Color=00FF00FF,range="0030-"0039]{Linux Libertine O}
\setmathfont[Color=00FF00FF,range="1D7CE-"1D7D7]{Linux Libertine O}
\setmathfont[Color=00FF00FF,range=\mathbf]{Linux Libertine O}
\usepackage{siunitx}
\usepackage{booktabs}
\begin{document}
\end{verbatim}
\begin{tabular}{l@{\quad}l}
\toprule
\verb|\LaTeX|&\LaTeX\\
\midrule
\verb|123|&123\\
\verb|\(123\)|&\(123\)\\
\midrule
\verb|\num{123}|&\num{123}\\
\verb|\(\num{123}\)|&\(\num{123}\)\\
\midrule
\verb|\num[detect-all]{123}|&\num[detect-all]{123}\\
\verb|\(\num[detect-all]{123}\)|&\(\num[detect-all]{123}\)\\
\midrule
\verb|\bfseries\num[detect-all]{123}|&\bfseries\num[detect-all]{123}\\
\verb|\bfseries\(\num[detect-all]{123}\)|&\bfseries\(\num[detect-all]{123}\)\\
\midrule
\verb|\bfseries\(\num[detect-all,detect-inline-weight=text]{123}\)|&\bfseries\(\num[detect-all,detect-inline-weight=text]{123}\)\\
\verb|\bfseries\(\num[detect-all,detect-inline-weight=math]{123}\)|&\bfseries\(\num[detect-all,detect-inline-weight=math]{123}\)\\
\midrule
\verb|\boldmath\(\num[detect-all,detect-inline-weight=text]{123}\)|&\boldmath\(\num[detect-all,detect-inline-weight=text]{123}\)\\
\verb|\boldmath\(\num[detect-all,detect-inline-weight=math]{123}\)|&\boldmath\(\num[detect-all,detect-inline-weight=math]{123}\)\\
\midrule
\verb|\boldmath\(\num[detect-inline-weight=text,mode=math]{123}\)|&\boldmath\(\num[detect-inline-weight=text,mode=math]{123}\)\\
\verb|\boldmath\(\num[detect-inline-weight=math,mode=math]{123}\)|&\boldmath\(\num[detect-inline-weight=math,mode=math]{123}\)\\
\midrule
\verb|\boldmath\(\num[detect-inline-weight=text,mode=text]{123}\)|&\boldmath\(\num[detect-inline-weight=text,mode=text]{123}\)\\
\verb|\boldmath\(\num[detect-inline-weight=math,mode=text]{123}\)|&\boldmath\(\num[detect-inline-weight=math,mode=text]{123}\)\\
\midrule
\verb|\boldmath\(\num[detect-inline-weight=text,mode=math,math-rm={}]{123}\)|&\boldmath\(\num[detect-inline-weight=text,mode=math,math-rm={}]{123}\)\\
\verb|\boldmath\(\num[detect-inline-weight=math,mode=math,math-rm={}]{123}\)|&\boldmath\(\num[detect-inline-weight=math,mode=math,math-rm={}]{123}\)\\
\midrule
\verb|\boldmath\(\mathbf{\num[detect-inline-weight=text,mode=math,math-rm={}]{123}}\)|&\boldmath\(\mathbf{\num[detect-inline-weight=text,mode=math,math-rm={}]{123}}\)\\
\verb|\boldmath\(\mathbf{\num[detect-inline-weight=math,mode=math,math-rm={}]{123}}\)|&\boldmath\(\mathbf{\num[detect-inline-weight=math,mode=math,math-rm={}]{123}}\)\\
\midrule
\verb|\boldmath\(\mathbf{\num[detect-inline-weight=text,mode=math]{123}}\)|&\boldmath\(\mathbf{\num[detect-inline-weight=text,mode=math]{123}}\)\\
\verb|\boldmath\(\mathbf{\num[detect-inline-weight=math,mode=math]{123}}\)|&\boldmath\(\mathbf{\num[detect-inline-weight=math,mode=math]{123}}\)\\
\bottomrule
\end{tabular}
\begin{verbatim}
\end{document}
\end{verbatim}
\end{document}
small_analysis.pdf
Description: Adobe PDF document
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