i found the onboard dac of the h390 to be excellent, as good as well reputed outboard dacs in roughly the sub $2000 range (think dena pontus, upper soekris, better w4s and so on), sonically it is on the clear and precise side, not romantic or particularly warm, very extended highs with a good amount of treble energy, expansive imaging, a sound most would call ’linear and accurate’ (even though in reality in this pursuit accuracy is never an objective term)
i tried running the h390 with outboard dacs, and it became clear to me that coming into the h390’s analog inputs (whether rca or xlr) the amp section sounded warmer and touch more rolled off and ’forgiving’ than with a digital feed through the onboard dac
this leads me to surmise that bent holter and team optimized the onboard dac to sound very clean, and synergize with the slight softening of the treble they built into the analog section of the amp
the midrange and bass in all cases was absolutely exemplary