First off are you hearing any distinct buzzing or popping noises, or are you just looking to clean up the backround noise as much as possible?
A majority of gains comes from disconnecting the USB power supply and feeding the device from a dedicated linear power supply. Second is isolating the ground line from the PC, and third is isolating the two data lines.
I've not used, nor can i find a pic of that unit with the heat shrink removed but i'm going to bet the power supply section is less an ideal for feeding an Audio Device.
From what i can see googling M1 DAC your unit has its own dedicated power supply with a decent amount of mains filtering so i suspect the USB power feed isnt required for the device to function. To test that theory i would sacrifice a USB cable by cutting it open and cutting the black and red wire, basically disconnect the power supply lines from the PC. Then connect the cable to your DAC and test A) does it still get recognized by the PC and function, and B) is there any audible difference in backround noise. I've also seen people suggest using bits of paper inside the plug to isolate the power pins in order to test the above, whatever works for you.
The results of the above will give us a better idea of what you need, plain isolator, or isolator with a dedicated power supply.
I documented some of my own Isolator build which is more focused on creating a super clean power supply but it may be of interest ->
http://www.head-fi.org/t/684459/usb-isolator-build