Bob,
Thanks for your suggestion.
Playing with ideas, I could also change to more efficient floor standing speakers, which maybe be one of the better approach for me in term of getting sonic upgrade and keeping my system simple.
However, I do like my C1 speakers, so I will not make any hasity move. Trying a sub as you have suggested may be the most pratical way of making improvement. Any suggestion as to what sub(s) to try?
Robert