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.
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.