Latex: long table twocolumn mode with xtab

gistfile1.txt

% \usepackage{xtab,afterpage}
\begin{center}
  \topcaption{Top caption xtab} 
  \tablefirsthead{\hline \multicolumn{1}{|c|}{\textbf{Command}} &
  \multicolumn{1}{c|}{\textbf{Effect}} & \multicolumn{1}{|c|}{\textbf{Extra}}
  \\ \hline }
  \tablehead{\multicolumn{3}{c}%
  {{\captionsize \tablename\ \thetable{} -- continued from previous page}} \\
  \hline \multicolumn{1}{|c|}{\textbf{Command}} &
  \multicolumn{1}{c|}{\textbf{Effect}} & \multicolumn{1}{|c|}{\textbf{Extra}}
  \\ \hline }
  \tabletail{\hline \multicolumn{3}{|r|}{{Continued on next page}} \\ \hline}
  \tablelasttail{\hline \hline}

  % \begin{xtabular}{ccc}
  % for custom column width:
  \begin{xtabular}{@{\extracolsep{\fill}}|*{3}{p{1.8cm}|}}  
  column1 &column2    &column3  \\
  column1 &column2    &column3  \\
  column1 &column2    &column3  \\
  \end{xtabular}
\end{center}

% Spanning over the two columns. 
% Problem: no text in the same pages of the table.
\afterpage{\onecolumn
% {\onecolumn  % in case of not using afterpage...
\begin{center}
  \topcaption{Top caption xtab*} 
  \tablefirsthead{}
  \tablehead{}
  \tabletail{}
  \tablelasttail{}
  \begin{xtabular*}{.8\textwidth}{c@{\extracolsep{\fill}}ccccc}
  \hline
  column1 &column2    &column3    &column4    &column5    &column6\\
  column1 &column2    &column3    &column4    &column5    &column6\\
  column1 &column2    &column3    &column4    &column5    &column6\\
  \hline
  \end{xtabular*}
\end{center}
\twocolumn}