You can spend a great deal of money on a DDC these days. It seems that DDCs are audio’s new "flavor of the week."
First things first: why to bother with DDCs, or their more primitive precursors, SPDIF converters?
1 - 10+ years ago when I got my first Musical Fidelity SPDIF converter (VLink 24/96), most DACs had rather poor, non-galvanized USB input implementations. So when I first started running the USB cable from the computer to the SPDIF convertor, then running a high quality coax cable to the input of the DAC, the sound got better immediately. I never looked back. BTW, I also tried optical and found it sounded rather brittle.
2 - A great many DACs still have rather mundane (not over-built & over-engineered) USB input boards.
3 - Recently I became interested in a DDC. I didn’t want to pay >$500, which left out most of the hot DDC brands du jour. I settled on the Matrix Audio X-SPDIF 2 for 3 reasons:
a. I own other Matrix gear and know them to be well designed and manufactured
b. I could buy it from Violectric’s US distributor, Arthur Power (a number of good experiences w/Arthur over the years)
c. And this particular DDC will run on either 5V USB power (ie, w/o external power) or can be powered via walwart.
I installed this DDC in place of my current SPDIF converter (Musical Fidelity VLink 24/192) running signal into the MHDT Labs Orchid DAC (NOS). I heard an immediate improvement in sonics--not earthshaking, but meaningful, including better separation of intstrument & voices, slightly more depth in soundstage, and slightly blacker backgrounds.
Net/net; I’ve demonstrated to my own satisfaction that an affordable DDC is well worth having.