I want to report a bug with this card. It says you can summon a NumberC or a CXYZ using only 1 monster (or more) from any graveyard. Thus, you should be able to use it with only 1 monster or with monsters from just 1 of the graveyards.
However it's impossible to use it with just 1 monster or when your opponent doesn't have the required Xyz monsters in his graveyard.

Have a good day.
RUM admiration of Thousands

Target 1 or more Xyz Monsters in each Graveyard, all of the same Rank; Special Summon from your Extra Deck, 1 "Number C" or "CXyz" monster that is 1 Rank higher than those monsters, and attach those monsters to it as Xyz Materials. You cannot Special Summon other monsters during the turn you activate this card. You can only activate 1 "Rank-Up-Magic Admiration of the Thousands" per turn.

Opps, my bad. Guess I missread ^^"
Thanks for the reply 🙂