I'm a little confused about this SD stretching. I have my receiver set to Native and on my SD channels they don't appear to be stretched. When I had it set to 1080i they would look stretched but now on Native I have a small (about 2 inches) black bar on the left side of my set. I can adjust this with my RPTV service menu although it may leave an inch on both sides when I center the image or if there's 2" or more poked under the right side then I'll have a full screen.
Anyway... my Toshiba did a fairly good job of stretching with E* SD's but the VOOM receiver looks really good... again, really not even looking like it's stretched.