@bluethinker Here's what it states in the manual:
NOS 1 - With this setting the upsampling of the DAC 200 is deactivated and the analog output filter (lowpass) is automatically set to 60 kHz for sampling rates of 44.1 and 48 kHz. For higher sampling rates, the setting you selected under the Lowpass menu item is used.
NOS 2 - If you select this setting, upsampling of the DAC 200 is deactivated. The analogue output filter always has the value selected under the menu item Lowpass.
BEZ 1 is a Bezier interpolator combined with a IIR filter. This process produces a result very similar to an analogue system.
BEZ 2 is a pure Bezier interpolator – offering perfect “timing” and dynamics.
FIR 1 is a classic FIR filter with an extremely linear frequency response.
FIR 2 is a FIR filter with improved peak handling.
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I believe T+A pretty much include the FIR filters to show how much better the NOS, and particularly, their proprietary BEZ filters sound. In my experience, the three warmest are NOS1, NOS2 and BEZ1. The most detailed, neutral, and balanced with the most holographic soundstage is BEZ2 for me.
Most of my clients who have purchased a DAC 200 prefer the BEZ 2 filter, but a few prefer BEZ1 and some love the NOS filters.
At a very basic principle, T+A strives for emotional response... goosebumps, if you will. Their words, not mine. I've found their gear to be a really great blend of the best of both worlds of being slightly harmonically rich and natural and also having incredible, non-fatiguing resolution and clarity.
Hope this helps!