FWIW, I have owned both the Quad Artera Pre and the Mac C49. The C49 is better—more dynamic and refined. The C49’s onboard DAC is pretty good as you noted. However, as for pure transparency, I actually prefer the Topping A70Pro to the C49 for preamp function. If you place high value on transparency and detail, you owe it to yourself to try one of the Topping preamps or headphone amps (that can function as a pre). If “made-in-China” is something you avoid, try the Benchmark LA4, it was clearly superior to the C49 in my system.
Another good American preamp is the Bel Canto Pre5.