Has anyone hired cyrix7x86 on Ebay to "upgrade" their crossovers?

I exchanged a few messages with him but ended up building entirely new XOs myself. 

Thanks for your reply. My other question is if an "upgrade" translates to a noticeable difference in the quality of sound being produced by the speaker. I imagine that the component parts of a crossover do not deteriorate over time - or am I mistaken?Paul

My other question is if an "upgrade" translates to a noticeable difference in the quality of sound being produced by the speaker.

In my case, I experienced a substantial improvement in SQ. Greatly improved resolution and transparency being the most obvious benefits. But caution is advised as it's also possible to make things worse. One of my precautions was to make sure I didn't deviate from the DC resistance of the circuits.

I imagine that the component parts of a crossover do not deteriorate over time - or am I mistaken? 

Most capacitors, resistors and coils will last for many, many years (well, tortured use such as high SPLs *could* cook resistors). One exception is electrolytic capacitors which can drift with time. If you have relatively inexpensive speakers or if the crossover includes caps with high value capacitance (eg, >50 uF) chances are electrolytics are in there. From my reading, these typically last 10-20 years. They will continue to work but speaker performance may decline.

Thank you for sharing your knowledge. Now I have to find out if our friend on Ebay has considered the DC issue AND actually "ear" tested his crossover upgrade for the SL700

What was the result of the conversation with cyrix7x86 and did you get your crossovers done?
I hope he's legit as there is a real gap in availability for some of the services he's offering.

Whether he tests individual components before using them and whether he deviates from the original design are important details.  I can (and will) ask him directly, but hoping to hear from someone who has experienced the results.

speakers must be custom tuned to YOUR ears. 

I never did use his services. I decided I did not want to take a chance and mess with the already wonderful sound of my Celestions.