I'd make part of the side panel removable, just around where the driver is, on both sides of the box (to access both drivers) which should be easy enough. The CSX 10" drivers I modelled are only 10.8cm deep, and I have 19cm in the rear chamber - so about 8-9cm between magnet and back wall, should be a pretty easy job to get drivers out this way + have the complete 19cm clearance around the drivers to get to the screws on the other side of the driver.

I thought about zig-zagging the folds too, it ended up making the box higher though which was not acceptable for my constraints (well the only height constraint is ugliness! but thats reason enough).

That subhorn sounds interesting, I'm not sure I can visualize exactly what you mean though - so rear chamber and start of horn would be at the ceiling and it runs all the way down, kinda like a completely straight horn or maybe with one fold?

Adrian