A previous discussion included a statement about crossover components.

I hav3 been upgrading Xovers for over 15 years ,having owned a audio store 

and having techs work for me ,I discovered with electronics ,as well as speakers 

on average only 25%  actually goes into the product the rest R&D overhead and markup .. sadly you see many using Solen capacitors or far worse ,and ceramic resistors ,cheap inductors and speaker terminals gold plated cheap brass which is 3 x less conductive then Gold Copper which = 3 x more resistance and noise

st least start there the WBT next gen are only $40 each , and if you have whst I call fake bywire setup 4 terminals many just are internally connected then you get the crappy straps ,always buy or make quality jumpers i,you can hear the difference 

go to Humble homemade hifi capacitor test for starters judt to see quality .

Duelund are the Bentley of the bunch. Path audio resistors, or Mundorfs Ultra resistors with a heat sink ,inductors I like Jantzen open coil Big for woofers and mids Waxedpaper Copper foil inductors very close to Duelund inductors. 
I spent over $1600 just in Xover parts this is a mid grade build but better then anything at $40k in a speaker.

@audioman58 your posting in a previous forum is what inspired me to start this thread. Thanks for sharing your insight. @blisshifi thank you for the reference  to The Humble Homemade page-WOW, what a treasure.I am going to contact Spatial and find out if they offer the crossover upgrade for my M4's, and if not see if they will get me a copy of their crossover layout-not holding my breath on that one, but the worst they can say is no.....and i've heard that before.

This thread is awesome.  I too know crossover caps can make a big difference.  I personally feel they have enough of an influence or sway power to ‘make or break’ a system.  I second @erik_squires observation with the mundorf capacitors and I too prefer the mundorf m-cap classic MKP or the mundorf m-cap evo oil.  I read good things about clarity cap. I’ve had good experiences with audyn plus mkp capacitors.

...and I appreciate and thank y'all for sharing comments, links ( @blisshifi 👍 ), and the knowledge gained by experience I've not had...

Kudos, Gentlemen.

This is interesting. I responded to a thread asking about when speakers become hi-fi verses mid-fi and was excoriated for stating that my Klipsch Heritage speakers were easily modded in the crossovers, making them more palatable for me as hi-fi. Crossovers can always be made better depending on your other equipment and musical tastes. Spend 40 years building your system and have a rudimentary knowledge of electronics and the world is your oyster.