Hi Again! Searching on VGMdb I found this disc, and I think isn't in the web, and now I share to you this bonus disc, is "WELCOME 【U・SA！】" sung by the 9 girls of the character discs, and a other tracks sung by Takahiro called "Kimi to Swinging Night"
I don't know about the instrumental tracks listed on VGMdb, and the users comments in the post on Tieba say that aren't the instrumentals tracks on the bonus disc
Tieba post with the link in comments: http://www.tieba.com/p/4876719257
VGMdb: http://vgmdb.net/album/59260
Japanese tracklist:
01. WELCOME 【う・さ！】 (9キャラクター Ver.)
02. キミと Swinging Night
Romaji tracklist
01. WELCOME 【U・SA！】 (9 Characters Ver.)
02. Kimi to Swinging Night
Download, share, enjoy and... ... Megu is the best loli in dah world! (???)