The 5900 is no longer available to new customers, as of a week or two ago. Plenty of replacement ones, though.

Even replacement 5100 & 5800's for customers on Dish Care.

All SD equipment should be phased out eventually. Even for folks with no HDTVs yet the current slate of HD hardware is backwards compatible.
Backward not-very compatible that is.

I put my 6141 on S-video or composite output to a NTSC TV, and both left and right sides got chopped to about 10% on each side, making things not fully viewable. Station logos, for example, will be chopped in half.

I tested this on more than 1 set, to make sure that it is not my overscan issue on my CRT, so I also put it on an LCD wide screen monitor but input via S-video and composite. I tried to change settings, but there aren't any inside that I can think of to change.

So sure, if you don't mind things being cut off on the sides, you can say it is "compatible". To me, it is a poor fit. I will take a 2700 over this if watching on an SD set.

I take it you tried pressing the "format" button on the Remote.?