From
SoundFreaq, sponsored by Cavalli http://www.head-fi.org/t/702787/chord-hugo/8055
(This is specifically regarding the Hugo, but some if it also applies to Mojo.)
"Mathematically, you cannot add to a complete analog system and make it better. Unless there was something fundamentally wrong with the Hugo at the line-out. Which is not the case. The specs top most everything. And some specs by enormous proportions. You can't add a lower performing anything and make it operate on a higher level. And simply, there are inherent and inevitable flaws associated with attaching another box electronics
of any caliber to the Hugo's signal, it is not the best use of the signal!
But some people will dig the character it adds to the sound. And
that is fine, as long as you understand that picking up any extra gear to add to the output is actually only adding flaws, and you're tweaking coloration. The whole point of hi-end audio is to get out of the way of the music. Leave it as simple and pure as possible. Adding loads of electronics in the form of an amp is the antithesis of this concept. An amp adds alot. It really does."
At the end of the day it is up to you. If you like the way it sounds, then you like the way it sounds. I would however suggest that if coloration is what you are after, then a tube amp will in most cases introduce a more pleasant coloration than a transistor amplifier.
Also, if you really think that "it gives a much wider sound stage to my ears. And so the impression of details/instrument separation increases" then you should buy another one, plug your first one into that and your headphones into the new one. Then when you have more money buy another and so on and so forth. When you have 10 or so connected together you will surely be blown away by the width of the soundstage and instrument separation.
Finally, when you are sinking hundreds of $ into components that may or may not bring anything positive to the table, then do yourself a favor. Learn something about how these things work, things like power supplies, output devices, balanced implementation, volume control implementation, etc. It will make this hobby more satisfying.