Even if Roxas couldn't tell him, he'd try. Because his friends did the same for him. It may have not meant a difference then and there, but in the long run it certainly did.

"That's what you should do! Honestly, everything about you, from your voice to your performance to what you can do on the instrument you're playing is pretty good. You should share that talent with other people. They'll appreciate it. It'll only be a matter of time before you get your instrument back. When you do.. oh man, the world better look out!"

He isn't even saying this in a joking matter.. not that Roxas would, because that isn't in him. But he really believes this, seeing and hearing firsthand what Demyx can and does do.