Re: StudioLive 16:4:2 troubles
Sounds to me like the power supply inside is just weak. The only thing that should matter though for rail voltage is how much output (aux and mains) and how much phantom you are using. These should be the only variable loads for the board. Slight power fluctuations could worsen the effect.
The number of channels/groups should not matter if the board is truly digital (as long as you are not driving any channel inserts or group outs as well, I don't know if the StudioLive has these or not).
IMO, this is completely unacceptable for a mixer targeted for live sound production.
Edit: one thing to note, the load on the outputs should not be that high. You are probably driving something with an input impedance near or greater than 10 kOhms. Even at +20dBu you are looking at 7.75V and about 6 mW.
