It's been a while but how about something like this ...
Basically this gives you a reference to the IDispatch of the underlying object, then you can call any method/property the object supports.
Dim o As TObject
Set o = Object("Name=grdBalances ClassName=dxDBGrid Index=2")
columncnt = o.Columns.Count
Or you could do this instead (a variation on your code), note the last line.
Dim oGrid As TActiveX
Set oGrid = TestPartner.ActiveX("Name=grdBalances ClassName=dxDBGrid Index=2")
columncnt = oGrid.Object.Columns.Count