Stereophile's test measuremets for the BAT VK-3iX state:
"The unbalanced source impedance varied from 7k ohms at 20Hz to 1460 ohms at 1kHz and 2650 ohms at 20kHz, while the balanced figures ranged from a very high 14k ohms at 20Hz to 1850 ohms in the midband and above."
7k ohms would be too low for the MHDT Labs 800 ohms output impedance, and would likely result in weak bass performance.
Of course, the test measurements may or may not correspond to your BAT preamp, but this gives you an idea.
The Burson Buffer would correct the mismatch.
Another option would be to try the MHDT Labs DAC into the BAT's balanced inputs using adapters.
"The unbalanced source impedance varied from 7k ohms at 20Hz to 1460 ohms at 1kHz and 2650 ohms at 20kHz, while the balanced figures ranged from a very high 14k ohms at 20Hz to 1850 ohms in the midband and above."
7k ohms would be too low for the MHDT Labs 800 ohms output impedance, and would likely result in weak bass performance.
Of course, the test measurements may or may not correspond to your BAT preamp, but this gives you an idea.
The Burson Buffer would correct the mismatch.
Another option would be to try the MHDT Labs DAC into the BAT's balanced inputs using adapters.

