The Hell rings are for mist users. If Lancia's boss' ring is a Hell ring, then Tsuna would have the mist attribute and I don't see that happening. :x
and I think all 7(?) of the Hell rings are shown in the manga. Although I can't be bothered to go back and look for it, none of them really resembled Lancia's ring. Unless Lancia's ring had something to do with the 'hell' of modern days. (666 or a skull or something)
what i ment was that it is a ring like the hell rings and not accually one of the hell rings. so it would be like a sky ring amp. which could make the x-burner stronger or something like that.