On these cheaper amps the RCA out is simply routed through the TRS jack connector.
This amp has 6.3 and XLR so that method is not available.
It would require an extra switch.
I believe the main purpose here is headphone out, and actually the 'magic' is only present on the XLR out, not on the SE out (and thus also not on the outputs on the back side)
The whole idea of this amplifier is the 'Halo' circuit which ONLY works on the XLR-4pin output on the front.
There appears to be a 2ohm resistor in series with the drivers (the - connections) and the voltage across that is also used as feedback or is used as an insert for an additional signal. They are, of course, a bit vague about that.
This means the TRS Jack output will always be 'normal' but the frequency response of the XLR may differ depending on the impedance of the headphone.
So the measurements on the XLR4 out can actually only be done acoustically via a headphone test fixture.
Amir could do such a test when he has balanced headphones (with XLR4 connectors).
This amp thus differs (on XLR4 only) from other amps and is the major selling point. Not the TRS out nor the pre-amp out.
If I had any balanced cables or headphones I would gladly take them up on their offer:
Try For Yourself; Measure For Free
Want to try Halo? Plug in to the front panel XLR. Compare to the front panel TRS, which doesn’t have Halo, because Halo requires separate ground returns. See what you think. We’ll also go further: if you have an acoustic measurement rig and want to publish your results (positive or negative, we don’t care), contact us and we’ll get you a Midgard to measure.