You see, I was discussing ctr-httpwin a few days ago here and some dude rejected it stating that it won't work on system transfers.
Anyway, IMO I think it's much simpler to just update the 3ds to v11.1 then do the DSiWare downgrade rather than using ctr-httpwin, especially to those new in the scene.
Target Unit can also use ctr-httpwin via the browserhax.How about the target unity? The source unity you may use ctr-httpwn since you already have HBL. But the target unity should have ctr-httpwn to receive the system transfer and you can't do that if your unity is on 11.0 or 11.1, right?
Anyway, IMO I think it's much simpler to just update the 3ds to v11.1 then do the DSiWare downgrade rather than using ctr-httpwin, especially to those new in the scene.