Thanks for the speculation, guys. I wish there were a place for me to talk to others who had experience with this underroasted stuff - I only ever saw it marketed at this one coffee shop and it has always seemed pretty mysterious. Actually, another coffee shop started selling it but I believe it's probably more of an inbetween blend and tastes more like roasted coffee. I may try picking up some of theirs.
I'm used to how it turns out in a proper espresso machine - both from the coffee shop I got it, and when I made shots myself with my manual espresso machine... The shots were always very pale tan and had a nutty taste that was very mild with no bitterness. In this case additional bitterness in shots is not wanted, because it doesn't have the rich taste to balance it out. It's been marked as "less acidic/more caffeine" and really only used in latte drinks, not for flavor itself.
I actually have been making all my coffee in the AeroPress with around ~170. I can try hotter, maybe it's needed to penetrate the hard beans. There's no way, at least with the blend that I have, that you can get anything close to an espresso grind - it's grainy chunks, and preground, because it will break grinders. My grinder is too nice for me to want to experiment
I wonder if doing a double press would work, much like second steepings of tea, could flush out the bitterness?
I can post updates if you guys are interested, since with no espresso machine in the immediate future I'm just wasting the rest anyway