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.
