The times I've needed TV2 to be on a lower channel number I either (a) ran things thru a VCR and outputted things (keeping the VCR on) on either channel 3 or 4; or (b) I swapped TV1 with TV2 and used the RCA jacks of TV2 into the television next to the receiver, and then used TV1 outputs to feed to the distant television (had to use two UHF remotes in this instance)
If you put the recievers modulation output to "Air" mode instead, you can reach most numbers below 70, or you can do like the previous post and put it through a vcr. Why do you want it that low? Usually worse quality.