I don't think you'll get everyone to agree on the wording and I think individual letters would be better in some ways. My advice would be to keep your letters as brief and to the point as possible, as long as they mention: 1) you bought the set for the OUT; 2) you'd buy it again on an HD format. Sending the discs back is an unequivocal insult to the SE and enough of a statement of displeasure. I don't think snide comments will help in any way.