Denon 888 - 4:3 hdmi input -> 16:9 output

I just picked up a SA 4250HD cable box. I connected it to my Denon via hdmi. I am with Videotron in Montreal if that makes any difference.

Previously, I had a SD cable box connected via s-video and set the Denon to output all video to the tv as 16:9. Now, with the new HD box, and having not changed that setting; the SD channels (broadcast in 4:3) are being output as 4:3. Very not cool!

Is this a limitation of the Denon and the hdmi connection? Would I get the widescreen stretch back if I connect the HD cable box via component? If so, what would happen to the HD channels broadcast as 16:9?

Thanks!

Yes, I want the source (cable feed) to get stretched from it's original 4:3 format to 16:9, to fill the tv. That's how it was before, and the Denon has a setting that does just that; but it no longer works.