Since you seem to have some know how before I did anything else I'd compare the the resistance of each driver to it's equivalent driver on your working speaker. This could be the reason you x-over is failing. If these are close then depending on your comfort with electronics I'd do one of two things (maybe both):
1) find out if Axiom would repair your crossover inexpensively. Much cheaper to send them just the board.
2) If you wanted to repair it your self and you have the equipment and know how then ... then I'd compare the x-overs to each other. You can measure the impedance of each component with a cheap LCR meter. Or compare the x-overs with a signal generator and scope. Try and find an exact replacement part for any bad component (including tolerance).
If you opt for #2 ... Hopefully you have an interest in this sort of stuff and the time. Money wise your still spending a few $. Note you will pay a premium buying parts in single quantities. Online try parts-express.com, digikey.com, or amazon (you'll need to check anything coming from amazon .. returns are free if the item is not what was described) ... google will come up with a few more ... local brick and mortar are even more expensive but google around and you'll probably find something.
Good luck
P.S. Mojo does have a good point ... the M3v4 is a pretty nice speaker ... and it might be worth your while to check out the refurb/B-Stock store at axiom (especially if you can wait for a sale which can be applied to it).
