I auditioned the 430HA at a local shop with relatively quiet listening conditions and wound up staying for over an hour. Simply marvelous; I was that hooked on the sound. I brought my own modded HE-6, and also listened with an HD800, Abyss, and a couple other mid-fi options. My sources were their in-house server, and my own laptop with a NuPrime uDSD feeding the coax input.
There was as SimAudio rep in the store at the time and we chatted for a bit, and he followed up with an email to answer some of my questions. I think some of it is relevant to all our interests so I'll copy it here (edited to remove any "sales/promotion" talk):
The amplifier operates using a proprietary topology where most of the gain is made in transconductance mode, but at the very end of the output stage it is converted back into a voltage output and thus avoids any weird behavior with load impedances as you were hinting at.
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The transconductance section in the Nēo 430HA is an in-house discrete design optimized for the best audio performance.
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Let say you start with a digital audio source in the Nēo 430HA; the signal will be balanced right from the very beginning of its analog life, straight from the DAC + and - outputs, and stay balanced for the whole signal path, including volume control circuit, up until it reaches the XLR pins on the front panel. Now for a deeper understanding there are the nuances between balanced differential as opposed to bridged configuration, and all of this is subject to debate. However, based upon what I feel is your definition, the signal path is fully balanced differential up to the output stage where it then reaches a bridged configuration comprised of independent but identical circuits.
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There is one DAC board in the Nēo 430HA, so all digital-to-analog conversion happens there. Many parts are shared between the two working modes, but the DSD is processed natively and is not converted to PCM prior to analog conversion. This board is not based on any other MOON product. This DAC engine will shortly be offered as an upgrade DAC option on other products too.