You need a reference audio source for the v3. It could be music, or white/pink noise. However, getting the balance close may be easiest with a white/pink source. You may want to use the same channel source for each channel of the minime; that way you won't have to worry about upstream variations.
Crank the v3 gain until it is peaking where you want it (based on the v3 meters). Then adjust the trim of the minime until it is peaking where you want it (based on its meters or your recorder's meters).
Once you do that, you should be set.