In the 2 months it has taken me to get through this thread I have tried a bunch of variations on this recipe in little 1 gal batches to see what I liked the best, all of which have come out pretty good.
My favorite so far is a batch where I doubled up the c120 and used a dark DME with about 3 peaches cut up and thrown in the fermentation vessel. For the juice I used apple juice concentrate and cranberry concentrate (which is strange because I really can't taste the cranberry at all) Used cascade hops and Notty yeast. Tried the same recipe with 1 lb frozen strawberry and that one is still pretty tart after being bottled for about 2 weeks, if its anything like the other ciders I have done with strawberry it will mellow out and be pretty spectacular with some more age. Both of these I let ferment out completely then used concentrated apple juice to provide the carb. I think I used about 1/3 cup per gallon.
I also tried a pumpkin version with 1 can pumpkin and about 1/2 a small container of pumpkin pie spice in 1 gallon. Added 1 cup brown sugar and used Amber DME with half whole foods cider and half concentrate. Really liked this until I put some cheap vanilla extract in there which gave it a bit of a funky flavor (still drinkable just not as good) I might forgo the pumpkin in the recipe as it took up a lot of space in the carboy and I don't think it added a whole lot of flavor. With the pumpkin I did two gallons and compared S04 to Notty. Couldn't tell a whole lot of a difference in flavor however the S04 seemed to ferment faster, and when racked slowed fermentation quite a bit more then the Nottty. When I bottled them (stopped around 1.02-1.01) I had to bottle pasteurize the Notty in about 2 days, the S04 took about a week to carb up appropriately.
My latest experiment is using the second runnings of some Heffe grains with about 3 cans of AJ concentrate in a gallon and weistephaner yeast with Haulatrau hops. Samples taste more like beer then graff so this will be interesting. I am thinking it will be more like a Heffe with a bit of apple in it then graff.
All in all this seems to be a pretty forgiving concept as everything I have thrown at it has turned out pretty good. As I said the peach seems to be a GREAT pairing to this and when I scale up to a 5 gal (in the next few weeks, want to see how I like the weistephaner yeast finished) that will definitely be in the mix as well as a good mix of dark specialty grains.
To the post above-give it some time, the tartness will subside. I have sweetened with apple juice concentrate, honey, brown sugar etc. I have heard of people using unfermentable sugars (lactose, splenda etc) or just putting some unfermented cider in there but age does wonders mellowing this out.