I took lots of pics during NX-3 Tower cabinet construction. Someone let me know how to post pics and I will.   When assembling the crossover will need to mount them on a big perfboard or something.  Is it best to avoid big metal terminal points?  I got the optional (giant) capacitors, and it looks like 3rd order filters?  A bunch of coils and caps.  first idea was to put the low pass section at the "bottom" of the main cabinet, and the High pass section below in the transmission line, but I need to work up an actual size plan on a piece of cardboard and see where I can place it.
Alternate plan would be to get more tube connectors, bring leads out for the woofer(s) and a set for the planar tweeter and house the crossover in a box behind the NX-3.  This ideal when adjusting the crossover, but I don't think I will need to get at these, but if back and front are glued on I would never be able to access the lower HP section, so I may have to have a removable panel?   Still thinking it.
I built my NX-3 with 3/4 MDF, cutting each piece to precise dimensions listed.  This is for simple butt joints.   I used Gorrila Glue, coating both surfaces and the clamping it secure for an hour or more,  I got to buy a Jasper circle cutting jig for my router and made the cutouts and recess for tweeter flange real easy and clean. 
I don't trust MDF glue joinery, so after everything was assembled (except the backs) I drilled and installed 40 dowels in each cabinet to add structural strength.