Well, it does indeed work fine with the 32 bit version.
I tried the following: $sFilePath = "C:\test.xlsb"
$oExcel = ObjCreate("Excel.Application")
$oExcel.Visible = 1
$oExcel.WorkBooks.Open($sFilePath, Default, 0, Default, Default, "m")
This works fine with 32 bit Excel, works from a script with 64 but Excel, but fails when compiled with 64 bit Excel.
Is this what you mean by using the native Excel COM? I tried looking around but couldn't find anything that suggested otherwise...