I've tried using the DAC1 on both my laptop (macbook pro via optical) and Marantz CD52 MK2 CDP and I have to say I can't agree with your opinion. Both of them are kinda low-end source but they sound huge different via DAC1. That's why I think to upgrade my CDP to a higher grade one.
As well as I saw a couple of fellows in Head-Fi use 3K+ CDP with their DAC1 or Apogee Mini-DAC. So I guess DAC1 can benefit from good transport.