It was obviously clear from the start the X4 allowed for more pleasing quality and tone. The session’s horns just didn’t seem to grate at my eardrums in the same way, they were all more polished, rounded, and the sound was less harsh. I already use valves in my Luxman LX-380 integrated, but the effect of adding the X4 was comparable from going solid state to tubes.- Buzz Hughes, HiFi+
If you wear headphones when you watch this you can hear the difference when the A/B compare, even through a low res youtube video: