Benchmark DAC 3 HGC or RME ADI-2 DAC

In your place I'd order both from an online pro dealer, compare them in my own system, keep the one I like more and return the other.

Both are dead silent, high resolution, low distortion designs, with the Benchmark having a few dBs lower noise floor, but it's of no consequence to sound quality.

If you plan on driving the amp direct the RME offers a 6.5dB lower max analog level compared to the Benchmark (+1dBu vs +7.5dBu @ 0dBFS on the XLR outputs), so with the Benchmark you might have to use more digital attenuation depending on your listening level and the whole DAC-amp-speakers gain structure.

No, the Benchmark's HGC is hybrid in the sense that its analog inputs are kept analog and the volume control is done in the analog domain, while for its digital inputs the volume control is done in the digital domain. So there is no AD conversion of the analog inputs.

Both the RME and the Benchmark (for its digital inputs) control the volume in the digital domain.

An advantage of the Benchmark would be that its analog inputs would allow you to use it as a preamp in the future if you add a phonostage or a DAC without volume control.

The DAC3 volume did not have enough granularity for me to be happy with it. It was rather coarse in the steps available.

This was with the digital inputs? I guess this is the penalty of using a pot. The RME doesn't have this problem as it uses a precise rotary encoder for VC which works in 0.5dB steps and the display also shows you the volume level.

Digitally controlled analog volume control just means there's a microprocessor or FPGA that controls the discreet resistor network or ICs used to attenuate the volume in the analog domain.

Other DACs with analog volume controls would be the Teac NT-505 and the T+A DAC 8 DSD.