Has anyone upgraded the crossovers on Spatial Hologram M4 series loudspeakers?

I haven’t done these speakers but have done others. Here is my guideline. If Erik Squires were here he has done more and has more cautions to add. I assumed the OEM designed a good crossover with the right frequency cutoffs but just didn’t use great components (because that is the dirty little secret of most speakers under $50-100K, they don’t use great components.). So I ordered components of the same values and wired them up identically.

I upgraded capacitors to the best Mundorf that I could afford--The EVO silver-gold-oil are excellent.

For the midrange and tweeter circuits of the crossover, I used Duelund Cast PIO bypass caps. I used .1uF, not the .01 that is often used.  edit to add:  your original crossover probably doesn't even have bypass caps.

For inductors I ordered custom copper foil beeswax from Jantzen. These are huge, heavy and expensive but worth it.

For resistors I used path audio in the treble and mid circuit. for the bass I needed more watts so I used a 30W Mundorf resistor with heatsink from partsconexion.

The caps are huge, the inductors are huge, and the resistors aren’t small so it became too hard to fit it all inside the speakers and I moved it outside. I built walnut boxes with plexiglass tops so nerds like me could appreciate the components and it turned out well. More importantly, it made a huge improvement in the sound quality.

Jerry

If I’m not mistaken, the Hologram M4s used 1st order crossovers with a single Mundorf cap on the tweeter/midrange dome. The woofers might not have a crossover at all and simply roll off mechanically. Regardless, unless you want to attempt a more complex crossover, there isn’t much that can be improved upon.
 

If you send one of your M4's to Danny Richie at GR Research, he will run his full battery of tests: frequency response, cumulative spectral decay---aka waterfall plot, crossover filters and parts quality, enclosure resonances, etc. He will then decide whether or not a x/o upgrade is warranted, and if so will design one. He does all this at no cost to you, just the price of shipping the speaker both ways. He has posted lots of videos on YouTube in which he shows the whole process.

Spatial maintains an audio circle forum where I suspect you will find someone who has done this. I’ve definitely seen upgrades on other spatial speakers there.

I try to approach speaker mods beginning with simple/cheap, and  progressing to custom-designed/built crossovers.

The quality of cabling and connection methods is often overlooked -- even by reputable crossover upgrade services.  Short wire lengths matters.  I like to use the same cable as the customer is using from amp -> speaker (because they already like the way it sounds).  Sometimes bulk cable is not available or very difficult to work with.  In this case, try to obtain something "similar" in design, materials, etc.  Bypass any spades and lugs and connect directly via silver solder. Persnickety?  Yes.  Audible.  Definitely.

A while back I was introduced to the concept of balanced/floating crossovers by one of the most successful speaker companies of the last decade.  Developed by a German speaker engineer and now used in the flagship models of the company that introduced me to it.  It is a VERY simple concept that improves detail, focus, dynamic contrast, etc.   I incorporate this design into all speaker upgrades.  If you'd like more info, I'll be happy to explain in further detail.  IF your speakers are 1st order, this would be easy to deploy.