Millenium dimode

First it looks solid and durable at first glance to me, but let's see how it ages.
Jack mono outputs are flat as expected, but the mixed XLR output has its response dropping in the high frequencies, with a -1dB~6kHz, -3dB~11kHz, -10dB~16kHz. A shame as I would think main use of such a device is to mix the stereo output of a computer, phone or such directly in a single input of a console... That is true that mixing stereo to mono is already not very clean regarding music applications, but maybe set the device in mono and use a jack output of the DI would be the cleanest then...? But to connect an amplug to a console for example that still works fine, as these very high frequencies are kind of useless regarding amp and cab sims anyway...
Also the -15dB PAD gives a ~25dB attenuation actually and not 15...