IMHO I would jump on it, if the price is right.
I have the S8's as fronts and S3 as a center. The C5 is a few steps up from the CC-690. The slight mismatch in front sound stage will be cancelled out by the large improvement in center sound quality and dialogue.
It's been a few years since I considered buying the C5. IIRC it was 'about' $3,300 when new.