Maybe he starts selling the tape when he's out of money and needs to buy fast food at family mart. :v
No, but really. I think more than to earn money, he made up the bands to seem more interesting to his fans. It would be fun to post a summary post on 2ch or something though. See how the Japanese fans would react lol
EDIT:
Also, in an interview with Pietoro of Da'vidshito:aL, you can read that he also confirms that he was part of the band Karma (along with Rietto). If the Darkside tape contains the same songs, then I guess Kisaki maybe he took their music as well (unless it's the otherway around, doubt it though)?
"We know that you joined Da'vid through Rietto who was your childhood friend, and before that you were a drummer, is that correct? Do you remember that band you played drums for? Pietoro: Karma, wasn't it? Rietto asked me to do support drums for Karma and we began to play together. Later I switched to vocals. I jokingly said: well, I'll sing It's the band that makes me remind of when I became a vocalist" (http://misashito.occult-proposal.net/pietorointerview.html)