For the boxes, which will be hidden anyway, I used a circular saw and free-handed it. Cuts weren't perfect, but very much good enough, and I didn't have to mess with setting all of the widths on my table saw.

If I was doing externally visible work, I would have used something more accurate, or at least attached a rigid straight edge to my material I am cutting.
2-M60s, VP180, 8-M3s, SVS 20-39PCi, DIY Sub, 8-Shakers, JVC RS45, Anthem MRX-1120