I think the S6 was the previous generation to what is current. Well regarded, but improved upon in the current iteration.
(I'm still surprised they haven't updated the Silver line considering the Gold and now Bronze has been refreshed over the last 2 yrs.)
Hmmm... as I look closer at the photos in your link, that doesn't look right:
The S6 may be an older model than the Silver 6...
there's this undated review, but the pic looks to be a match:
www.hifi-review.com
And here:
Monitor Audio Silver 6 Floorstanding Speakers user reviews : 4.3 out of 5 - 8 reviews - audioreview.com
www.audioreview.com
And this:
SEE NEW LISTING & PRICE. Item: Monitor Audio Silver 6 Speakers (Kimber Cable Jumper Cables negotiable). “Incorporating a 6†(150mm) C-CAM bass driver, a 6†C-CAM bass/mid driver, and a 1†(25mm) Gold Dome C-CAM tweeter, the RS6 is a svelte floor-stander, equally at home in stereo and mul...
www.stereo.net.au
I'd pass.