My local lumber company quoted $340 for a 4x8 3/4" sheet of Teragren bamboo ply and they had to ship it in. Each face of the sheet is 3/16" horizontal bamboo and the balance of the panel thickness was made of pieces on edge. Nice stuff but $300 over a sheet of MDF is a pretty big premium. A hazmat suit would be cheaper.
They also confirmed bamboo requires very sharp blades that will need to be sharpened frequently.
So maybe the title of this thread should have been "Bamboo Ply vs. MDF vs. Baltic/Russian Birch Ply". Baltic birch ply is readily available (I'll have to look for the specific kind Rick noted) and is a joy to work with but I just didn't think it was acceptable for speaker cabinets. Learn something every day!
Cost is as noted, about $50 for 5x5x3/4, and it would probably take three sheets for the Ottavos so it puts the lumber at less than 1/4 the cost of bamboo. And these will get veneered regardless of the cabinet material. So do the cabinets get braced any different between MDF and Baltic Birch?
Lastly, very nice looking speakers guys!