bad alignment when using xparse, tabularx and enumerate

I want to extract this piece of code into an environment

begin{table}[H]
  begin{tabularx}{textwidth}{lX}
    toprule
    textbf{a} & a  midrule
    textbf{b} & b  midrule
    textbf{c} & c  midrule
    textbf{d} & d  midrule
    textbf{e} &
    begin{enumerate}[leftmargin=*,label=arabic*),nosep,after=vspace{-baselineskip},before=vspace{-0.6baselineskip}]
      item x
      item y
    end{enumerate}  midrule
    textbf{f} & e  bottomrule
  end{tabularx}
  label{tab:table}
end{table}

Wanted usage:

begin{ucbx}{a}{b}{c}{d}{e}
  item x
  item y
end{ucbx}

I am currently using the xparse, tabularx, float, booktabs and enumitem packages:

NewDocumentEnvironment{ucbx}{+m+m+m+m+m}{%
table[H]
tabularx{textwidth}{lX}
toprule
textbf{a} & #1  midrule
textbf{b} & #2  midrule
textbf{c} & #3  midrule
textbf{d} & #4  midrule
textbf{e} &
enumerate[leftmargin=*,label=arabic*),nosep,after=vspace{-baselineskip},before=vspace{-0.6baselineskip}]
}{%
endenumerate  midrule
textbf{f} & #5  bottomrule
endtabularx
endtable
}

This code does not produce the wanted output and also throws You can't use relax' after the., Misplaced noalign., Undefined control sequence., misplaced alignment tab character &. and LaTeX Error: There's no line here to end. errors.

I am using XeLaTeX for compilation.

Current output:

Thank you.

documentclass{article}
usepackage{tabularx,booktabs,enumitem}

NewDocumentEnvironment{ucbx}{+m+m+m+m+m +b}{%
  begin{center}
  begin{tabularx}{textwidth}{lX}
  toprule
  textbf{a} & #1  midrule
  textbf{b} & #2  midrule
  textbf{c} & #3  midrule
  textbf{d} & #4  midrule
  textbf{e} &
  begin{enumerate}[
    leftmargin=*,
    label=arabic*),
    nosep,
    after=vspace{-baselineskip},
    before=vspace{-0.6baselineskip}
  ] #6
  end{enumerate}  midrule
  textbf{f} & #5  bottomrule
end{tabularx}
end{center}
}{}

begin{document}

begin{ucbx}{a}{b}{c}{d}{e}
  item x
  item y
end{ucbx}

end{document}