I noticed from the file DTAs_prod_list.pdf of energy star units that there are 5 versions of the DTX9950. Two draw 7.2w (no letter and "S"), while A, B, and C draw something less than 5w. A, B, and C have slightly different power draw, so there must be something different about them. The tests are as of 8/1/2008 for S,A,B,C and 5/1/2008 for no letter.
I recently acquired a 9950C (the letter is next to the bar code on the bottom label on the "c" unit). It is only warm after hours of operation.
In comparison with a DTT901, it pulled in one station the 901 did not, but didn't find one the 901 did. A channel that periodically breaks up on the 901 seems to be more solid on the 9950c. Passing airplanes disrupt both boxes on that channel. I use a fixed position roof top antenna.
I think the 901 has a slightly better picture. Fewer digital artifacts. On a 27in TV, if I didn't point them out, others didn't seem to notice the difference.
The 9950c remote is a little easier to use in the dark/without looking because of the shape and button arrangement. There are TV volume controls in addition to the converter box volume. The resolution of the volume control is coarser on the 9950 than the 901. 20 steps vs 100 steps if I remember correctly. If you need to get the volume down quickly (as in someone is sleeping and had the volume high before they turned off the box) the 9950 performs this function rather quickly. The 901 takes a few more (agonizing) seconds.
The power LED is more subdued on the 9950c, which is appreciated in the bedroom. The 901 LED is not bad, but much brighter. An artistically cut piece of electrical tape could easily "fix" the 901 glow
The 9950c unit is physically smaller than the 901. It happens to sit better on top of this particular TV.
I'll keep both of these units.