A simple review, this is the best amp I have ever owned. It has a ton of power, enough to drive virtually every headphone on the market, it sounds incredible. Even my Koss Porto Pros sound crazy good off this thing, so clean and clear.
Not only that you can drive 3 headphones at once if you want!
Crazy value, for 349 bucks you get all the power you need and state of the art performance. Buy this and never need another amp ever (unless you wanna go for tubes!)
It is definitely an upgrade over a Aune X7S but if you dont need more power and your headphones are high impedance the Aune X7s is a solid amp. Its biggest weakness is the 11 ohm output impedance on it, which means its not ideal for use with headphones below 88ohm impedance. If everything you are using is that or higher and the Aune gets them loud enough without distorting you should just be happy with the Aune!
However if you want more power and just the peace of mind of knowing that you have one of the best amps on the planet and can basically power any headphone you ever want to buy than the 789 is the way to go.