Channel 6 is already on Channel 6 on most Comcast systems in the area. I think systems near the antenna farm, 3, 6, 10, and 12 are on other cable positions back when analog cable used the same frequency. They did this so that you would not get the cable signal and some ota signal at the same time. Out here on the Comcast headend out of Malvern, channel 10 is on cable position 11.
6 hd is 806 and 10 hd is 810. I have FiOS, so it doesn't matter.