There are some used Vandersteen 2c's listed here. I had
Vandersteen years ago and I think they would fit the bill! One
thing for sure is they are not bright!"
I recommend the Model 2's as well, but if you are looking for a dull sounding speaker to offset what you have now, they are not it. Set up properly, they are more neutral than you're current speakers, and also have better bass. But they're more detailed. I wouldn't say bright, but they are not going to hide anything.
Looking at a picture of your Focal 826W's it looks like they have a very similar tweeter to the one's in my Wilson's. Wilson uses a Focal titanium tweeter like the one that's in your Focal's. It could even be the same one. Comparing that to the Aluminium tweeters that are in the Model 2's (current production) I have in my main system, the Wilson's are actually a bit more forgiving on the top end. And if it looks like I'm trying to talk you out of buying them, I'm not. Vandersteen is one of those speakers that you need to audition first. A lot of people comment that they are a warm/forgiving type of speaker. After 4 pairs, I have yet to hear that quality.