I've been enjoying the Aune x8 XVIII bt for some months now, the Dac that replaced the Toppings I had (a d90 for a few days and a d70s for a few months...I prefer the Aune). The main feature of the Dac (apart from the impressive value for money) is that the opamp is interchangeable, which I thought it was irrelevant in terms of sound...I was wrong. Placing a new opamp is extremely easy: remove two screws from the bottom of the dac, remove the original opamp with the tweezers that are included when you purchase the dac...and that's it.
I did some tests with the dac connected to my Burson Conductor (I really like its sound signature), the Aune xp2 linear power supply and my beloved Sony mdr-z1r headphones. Tidal master from a Windows PC, exclusive mode.
With the standard opamp (jrc) it sounds good, obviously. It is still a dac, the sound will not change like when you change your amp or, above all, your headphones. Afterwards, I've changed the stock jrc opamp for the burr-brown opamp that also comes when you buy the device. Perhaps it went from a neutral point to something more musical, but a barely perceptible difference.
Some hours later I've changed from jrc/bb to discrete premium opamps. I can hear some differences when placing the Burson and Sparkos opamps instead of the original ones.
When you get the Burson v6 vivid, the first thing that hits you is the size, It's massive, especially if you compare it with the jrc or the bb. This means that you have to install some dampers on the Dac, or anything that will make it go up a few inches. And in the case of the v6, which is twice as tall as the sparkos ss3602, an opamp extender to place it horizontally (Burson has one)
Setting-up is very simple. The opamp's legs are sturdy and go in with no problem (unlike the jrc or burr-brown ones, extra care when you operate with these opamps). Important thing: due to the Burson's own architecture, it doesn't matter how you place it. If manipulating the jrc, the bb or the Sparkos you don't pay attention to the notch (or the point) and you put them backwards (something quite easy if you don't take notice)...You will have to send the dac to the technical service.
Assuming that both the v6 and ss3602 are great products, they have a different sound signature. V6 vivid gives you a wider scene, a more lively sound throughout the spectrum (perhaps the most noticeable difference is in the treble). When there are many instruments at the same time, you notice more separation between them. With sparkos everything is more natural, softer, with less scene.
The differences between the standard ones with the premium ones is noticeable. It depends on your tastes. I prefer the Burson opamp, especially considering the music I listen to (80's pop and rock, edm). Maybe if I listen another type of music I would prefer the Sparkos.
The price of both is around 80 euros more or less. A considerable amount of money, but certainly worth it.
Pd: sorry for my english