[XeTeX] mathspec and MnSymbol

[Thierry]

Hello,
I have installed a prerelease version of texlive 2009 to test it.
Now I can play with a new version of xetex.
(This is XeTeX, Version 3.1415926-2.2-0.9995.2 (TeX Live 2009))

I would like to use the convenient package mathspec to choose my font in math mode, and at the same time MnSymbol to use their symbols.

My first question: is there any difference between
\usepackage{MnSymbol}
\usepackage{mathspec}
and
\usepackage[MnSymbol]{mathspec}?
Both works for me.

Second question, which is in fact a problem: 
with one of these two commands, I can't use
\setmathfrak{Lucida Blackletter}
I have the error:
! LaTeX Error: Command `\mathfrak' already defined.

I have made a test with all the other commands
\setmathrm, \setmathbb, etc given in mathspec.pdf:
Without MnSymbol, everything is fine. 
With MnSymbol, only \mathfrak 'is already defined', but using them all in the text gives me this error message:
! LaTeX Error: Too many math alphabets used in version normal.

Is there a solution to that?

Thanks in advance
Thierry