Zin & Sulhu used to join Xing 5th Generations before they debuted under the group X-5.
Zin's position in Xing was a rapper and a vocalist while Sulhu is only in charged for rapping.
I'm not really sure when did this group was formed but one thing for sure is that they released a teaser for their song 'Tears' around the end of December 2009.
Zin (Hyeonjin) & Sulhu (Jinwan)
XING 5th Generation - "Tears" MV Teaser
@0:44 sulhu & @1:24 Zin
Xing 5th Generation - Memorize
This song was originally sang by the previous members of Xing back in 2008 where they were consisted of all members of DNA (The Boss) and more.
Zin - @1:37, @3:11 & @3:23
Sulhu - @1:46 & @3:17 (Sulhu)