Anyone had the equipment customized ?

Yes; kinda, maybe, sort of.   Being a electrical design engineer, I design a log of amplifiers and analog control electronics at work.  So naturally, I do this at home with some of my equipment.  For a while, I was doing custom electronic design for folks who had high end stereos. 

The key is finding where the weak spots are in the equipment, then making those spots more robust.   By weak spots, I mean where the designer left performance on the table and didn't pack it into the product.   Anyone can tweak stuff, which may or may not sound better, and may not give you much bang for your buck.   And, trust me, hiring someone to do custom engineering on your equipment is expensive. 

If you go this route, pick someone who routinely modifies your brand and model often.   That is, they have a long history of fixing that particular model.   Ideally, they should be someone who actually worked at the factory or someone who worked in their service dept.  If they don't meet this criteria, don't send them your equipment or money!

When I was modifying equipment and making money at it, I found some horrible stuff that came in from folks who someone modify it but didn't know what they were doing.   One crossover came in the shop and the guy used acid core solder on all the connections.   Another had such bad workmanship, I had to rebuild the entire thing and fix it before I could modify it.  

If you go this route, make sure you go with someone who knows their way around an electronics lab and has impeccable workmanship.   Take a gander at some of the work they have done in the past and get recommendations.

That does make a lot of sense.  Rail to ground decoupling caps work much better at killing noise when they have a moderate amount of ESR in them while DC Blocking caps passing a signal work best when ESR is held to a minimum.  

That is the often thought philosophy.   It is a small amount of ESR, which dissipates the noise energy as heat, rather than dumping onto the ground plane and causing ground bounce.   Sure, a cap with large ESR can cause a spike on the chips power pins, what is needed is a small amount of ESR in a bypass cap to dissipate that spike as heat.     

Some large computer back planes have shunt VHF caps in series with a 1 to 10 Ohm resistor to ground just to keep the power plane resistive and lossy at higher the frequencies where typical bypass caps have gone through their internal self resonance.  

For series DC blocking caps, then, yes I totally agree, the lowest ESR cap is best.