Well, when I try labbing out C dash cancels, they appear to be pretty hard, especially after D amplifying it :P
Is it that you don't get your dash cancel to come out? or is it that you aren't able to connect an attack afterwards?
One thing to note is that you can't use the A+B dash macro for dash cancels. so you'll have to do a ->-> or <-<- input for dash canceling.
Other then that, you are able to buffer the dash input during hitstop so you can do it a lot earlier then you might expect.