Thank you so much for your kind words!
I definitely plan to add music and sound effects as the game develops. For these first updates my focus has been on the writing and art, but I also absolutely feel the void of no sounds and would like to add them soon. I've already found some good resources I may use.
To unlock Marco's first two CGs, choose to go check out the dorms instead of going to Matt's apartment. When you first speak with Riley for the first time, choose to go hang out in your room instead of taking Riley's tour.
When you go to your room, you'll run into Marco before he heads out. You'll unlock his intro image and then have the opportunity to fantasize about him, which are the two CGs you're missing :)