How do bi-wired speakers work? Can a two post speaker be modified to be bi-wired?

My NAD7600 has duel posts for bi-wireing but my ADS M15's just one set of posts. Regards, Mike Stevens
if two-post speaker has parallel crossover than it can be modified for bi-wired one otherwise it cannot.
bi-wired speaker basically setup to use a reactance value ranges of wires that are going from amplifier and has a parallel crossover thus using this reactance to match-up the best crossover point.
wires due to their reactive nature to the AC signals do have reactance that in some scale impacts crossover point
on any of the speaker crossovers.
I would not try to modify a speaker in this way. Your speakers were designed for one pair of binding posts. I would leave it at that.
I agree with Sugarbrie. To make your speaker "bi-wirable" would require changing the cross-over assembly, therefore changing the characteristics of the loudspeakers in question which is not, at all, worth the effort.