I think that Himem.sys can only reconigize 64MB by default, and in fact may be the upward limits of some versions of it.
I suggest trying the following:
1) Try using the version of Himem.sys that comes with Windows 98 or ME
2) Try loading CWSDMPI.exe WITHOUT loading Himem.sys to see if MAME will allocate XMS/Extender automatically
3) Try loading windows, and run AdvanceMAME from a windows Dos Box.
4) Try using WinMAME from a windows Dos prompt.
5) If none of the above will work, maybe try Linux.