Capacitor

ODAMs are spectacular.  Grannyrig is spot on with everything above. 
I used ODAMS in a Cornwall IV crossover upgrade project.  I also used them on the output coupling caps in a Manley Chinook. 
My sense is they allow more and better signal transfer.  They are a touch warm but the detail is natural and spooky realistic. 

I also like ClarityCap. They have great holographic spacing and spatialization.  They get large in size as you move up uF. 

Ugh. I’ve seen this on several other threads —people attacking capacitor upgrades in a high handed manner. 
I purchased a certain budget preamp that allows capacitor rolling with built in binding posts for caps on both output coupling and gain stages. It is $1k new abs I got it for about $600 used.  You can swap caps in a moment (once you discharge them safely). I bought this thing because it was easier than building something like it. 
I don’t need Raul to tell me anything. I’ve heard the sonic differences in caps.  Wima  are fine caps that do a decent job and meet spec. But they do not come close to things like VCap.  
Yes they are pricey things. A pair of great caps can set you back several hundred bucks. But the sonic differences are easily audible —more so TO MY EARS than a power cable, for example.  
While it’s true that some manufacturers just  use Wima or other decent caps, it’s also true that many do not. 
It’s also true to my ears that a decent 6 or 12 volt reissue preamp tube can sound great and quiet. So many get a bad rap yet manufacturers use them all the time. And it’s also true that some NOS tubes can sound magical and just better. It’s not practical to source them when building to a price point.   
Thanks to Granny and Charles for keeping decorum and encouraging folks to listen for themselves. 

You can change the value of an output coupling cap and do so safely and do so to better effect. But, as a general principal you want to stay near tolerances as designed.
Sometimes people violate rule no 2 above because they want to better match impedance between amp and preamp. Manufacturers usually try to pick a level that will match with a larger number of combinations yet you can customize this so the gear mates better. There are good calculators out there for this purpose.

Here’s a great calculator to use when matching output caps. 
http://www.v-cap.com/coupling-capacitor-calculator.php

Raul, I get your points. Well made.  Do you work for Wima?  
Just kidding. 
I do believe I hear better signal through two of the Vcap lines and others. I agree to disagree. 

Raul, I’m sorry. I’m having trouble tracking your points. Sounds like you tried other caps, liked them, and later found them to add too much color. So, you went to or back to a good quality Wima cap. 
I don’t hear material colorations with VCap or ClarityCap. What I hear is better spatialization, clearer pictures, and bigger more defined images. 
One of my favorite records is Lou Rawls and Les McAnn, They Call it Stormy Monday. I’ve listened to it at least hundreds of times. With Vcaps in the signal chain I can hear Rawls move his mouth in different directions while singing into the microphone. It was so spooky on discovery as it made me hear deeper into the recording and gave a stronger sense of realism across the experience.