Schiit setup troubleshooting

What had you been connecting the black (ground) wire in the Speakon cable to?

The manual for your sub does not provide a specific recommendation for connecting a single sub to monoblock amps having balanced/differential outputs, stating that they "strongly advocate" using two subs with monoblocks (whether balanced or not). However based on their recommendations for other applications of your sub, and on recommendations I’ve seen in other REL manuals, when you reconnect the sub you should first try leaving the black wire unconnected. And if a hum results you should connect it to a ground point on the preamp. Such as the ground shell of an unused RCA connector (using an RCA plug with the center pin unconnected), or perhaps to a chassis screw.

In any event, the black wire should absolutely not be connected to a red output terminal of either amp, and probably not to a black output terminal either.

Regards,
-- Al

I check my speaker<->amp connections last night and it turns out that they are connected correctly.

Is the sub still connected?  And can you indicate the specific make and model of the sub, and describe exactly how it is connected to the amps?

In any event, glad you have made some progress.

Regards,
-- Al

Is there any possibility that using a single-ended input into the Freya (in this case the DAC), then outputting via balanced XLR to the amps could be the cause of the issue?

After looking at the manual for the Freya S I don't see any concerns with that, given that you are using a Nexus mode.

Regards,
-- Al

I would definitely try disconnecting the sub altogether.

If I understand correctly you are connecting the two amps to a single powered sub (i.e., both amps are connected to the same sub, with the sub providing speaker-level inputs for two channels). If so, it is likely that there is a ground path within the sub that is connecting one of the two positive output terminals of each amp (the output terminal of the amp that I presume is connected to a negative input terminal of the sub) to the corresponding positive output terminal of the other amp. Which could very likely account for the problem. And that path would exist even when the sub is turned off.

Regards,
-- Al

First, just to make sure something simple isn't being overlooked, I assume you are connecting each speaker to the two positive output terminals of the corresponding amp, given that you are using the amps in mono mode. And I assume you have seen in the manual for the Freya S that it has a 60 second delay following turn-on.

Second, by any chance are the speakers AC powered (for example do they include a powered woofer), or do you have powered subwoofers connected to the amps? If so, the negative input of the powered speaker or sub may be grounding or excessively loading the signal on the positive output terminal of the amp to which it is connected, causing the amp to shut down.

Regards,
-- Al