I'm approaching the start of my third year with an SP20 and enjoy it very much. Cartridge matching was a challenge with that 58dB fixed gain. I spoke with ARC directly and was told to stay above the .5mv level, which led me to the Ortofon Cadenza Blue I have now on my VPI Prime. Your Delos is .6mv, I believe, which is really perfect for the SP20 phono stage.
You might have turn increase the volume setting a little from your current setup, but you won’t suffer any noise floor problems. It’s a very quiet component. My dealer wanted to sell me a Linn LP12 with that cartridge they had just released in the fall of 2015. It was like .25mv—well below the recommended ARC matching specs. But during our demonstration there was still almost no discernible noise from the phono stage.
You might have turn increase the volume setting a little from your current setup, but you won’t suffer any noise floor problems. It’s a very quiet component. My dealer wanted to sell me a Linn LP12 with that cartridge they had just released in the fall of 2015. It was like .25mv—well below the recommended ARC matching specs. But during our demonstration there was still almost no discernible noise from the phono stage.