I kept the bracing to a minimum with just 1 plywood window pane which helps square the box and a few pieces of pine 1x4 placed irregularly on the walls. The Arauco seems quite non-resonant and I wanted to try the Audio Note idea of letting the box flex somewhat.

The multi-layer approach you mention is well-regarded; the XLH was built from 3- 3/4" layers and we know how natural that sounded. And how heavy!

If you use plywood and no veneer cutting 45s and joining with biscuits then using a few band clamps is a great idea. Personally, I don't think all the box-within-a-box stuff is worth the trouble, but that's just me.