From the Massive Passive manual:
5) PHONE JACK INPUT. (Channel One or Left) Accepts balanced or unbalanced sources. Factory set-up for +4dBu pro levels. There
are some DIP switches internally that can change this to -10dBv semi-pro or hi-fi levels. The pin out is as follows: Tip = Positive = Hot,
Ring = Negative = Low or ground, Sleeve = Circuit Ground. If you use TRS plugs be sure that the ring is connected to the negative or ground
and not "open". Input impedance is 20K ohms. See page 16 & 17 for the DIP Switch details.
6) XLR JACK INPUT. (Channel One or Left) Accepts balanced or unbalanced sources. Only for +4dBu pro levels. The DIP switches
have no effect on the XLRs. The pin out is as follows: PIN 2 = Positive = Hot, PIN 3 = Negative = Low or ground, PIN 1 = Chassis Ground.
Be sure that the PIN 3 is connected to the negative or ground and not "open" or a 6dB loss or loss of signal will happen. In general, the XLRs
and +4 pro levels are slightly preferable over phone plugs especially if gold plated matching XLRs and good cable are used.
7) XLR JACK OUTPUT. (Channel One or Left) Transformer Balanced and Floating. Only for +4dBu pro levels. The DIP switches have
no effect on the XLRs. The pin out is as follows: PIN 2 = Positive = Hot, PIN 3 = Negative = Low or ground, PIN 1 = Chassis Ground.
Be sure that the PIN 3 is connected to the negative or ground and not "open" or a complete loss of signal will happen. Output impedance
is 150 ohms and output levels can reach +37 dBv (hot) which may distort the next piece in the chain.
8) PHONE JACK OUTPUT. (Channel One or Left) Unbalanced output only. Factory set-up for +4dBu pro levels. There are some DIP
switches internally that can change this to -10dBv semi-pro or hi-fi levels (with a phase reverse). The pin out is as follows: Tip = Positive
[top] Hot, Sleeve
Circuit Ground. If you use TRS plugs be sure that the ring is connected to the negative or ground and not "open". See page
16 & 17 for the DIP Switch details.
Hope this helps
The King