I'm not the only person who has experienced this as Currawong had written about this in his written review of the Jotunheim 2, mentioning that out of SE - its not suitable for sensitive IEMs (such as the CA Ara he tested with) as he noticed both a significant hiss and slightly noticeable hum component (same experience as me). However for me, I find this extends to even sensitive headphones like the AD2000 and HD598SE. I can't hear any noise through XLR out with the headphones I have a balanced cable for, but SE output is significantly noisier. I'm feeding the Jotunheim with Modius through its balanced outputs, but the noise floor is the same even when using unbalanced. For comparison I also have the Cavalli Tube Hybrid (an SE tube hybrid amplifier) which to my ears has a significantly (but still slightly audible) lower noise floor than the Jotunheim 2 through SE. I've also tried the iFi Zen DAC and I can't hear any noise with that. Singxer SA-1 also has no noticeable noise from both SE and Balanced but that's to be expected from a top measuring amp, but I'd like to move back to Schiit as I prefer the sound of their amplifiers.
By all means the Jotunheim 2 is an excellent amplifier, and my favourite when I use the balanced outputs. But I believe because the Jotunheim 2 is a balanced differential amplifier, and optimised for balanced operation, I think they are only using part of the differential amplifier circuit to facilitate the SE output which has noise constraints (balanced differential operation allows cancelling noise components), while Asgard 3 and Lyr 3 are designed and optimised for SE operation. That's my rationale behind believing they would possibly have a better noise floor than the Jotunheim 2 in SE.
Will do, thanks! I'm keen to hear your findings