I have the M2 Tech Vaughn DAC that I purchased from a friend after replacing some PS caps that had failed in the unit. As you may know, the unit runs on battery power that gets charged when the battery runs low. Best digital I've heard in my system but unfortunately I've had problems. I've lost 3 of the 4 S/PDIF inputs and not sure why. The USB input is the piece de resistance of the unit but unfortunately it develops a small popping noise that gets progressively worse as time goes on so I stick with the BNC S/PDIF input via a PrimaLuna Prologue 8 feeding it. Also, the S/PDIF input will develop a static like noise and I have to pause the CD player several times to clear it. I am running the DAC and CD player from balanced power that is well filtered and grounded so I'm at a loss as to the noise issues but damn does the unit sound good!