Congrats Nick! Good luck in your building project. It is a process with a capital P, but always worth the effort when you get a nice new house at the end.
The non parallel sides are great for acoustics, same reason a lot of speakers have non parallel side walls, to minimize internal resonance due to reflections. For stereo listening you want it more lively than HT which can be more dead, so it's better to have the angles between the side walls and the front wall be equal so the stereo soundstage is balanced especially with a smaller front wall. But instead of one slanted front wall, you could make it two smaller, slightly angled (almost inline) walls, as long as everything is symmetrical down the centerline. One small wall built from the center of the front wall to a point on the side wall which comes off the acute angle to the front wall, in order to make the front of the room symmetrical. That would be a great stereo room. The rear wall's angle is not as important and can be made symmetrical or not, and can be treated with absorbtion to minimize reflections off the back. For stereo listening you could put diffusion on the back wall if you like a more lively sound. So non parallel side walls is ideal for stereo listening if you can keep it symmetrical down the center of stereo line. Great for HT too, of course.
Rich