Quickly checked spec of Adam A7v, max input level is +19 dBu, which is 6.904 vrms.
Your DX7 PRO has max output of 4.2vrms, so no problem here.
Read the spec -- 0 dBu = 100 dB SPL at 1 m for 0db setting.
Now, with -12db setting, you get 88db / 1m with 0dbu. And your DAC is able to output...