What Digital to Digital Converter Do You Use? Why?

Well, I just took the plunge and bought a Denafrips Iris DDC.  My Pegasus DAC shares some of its DNA with the Pontus ll, and the review of the Iris on The Audio Beatnik makes me pretty confident I’ll realize some significant benefits.  I was eyeing the new Musician Pisces DDC as it would obviously pair well with my DAC, but on further review the Iris and Pisces look like clones in specs and on the inside (maybe not all that surprising as like the Pontus and Pegasus they come from the same factory), and I was able to get the Iris used for $399 so that pretty much sealed the deal.  I’ll report back with comparisons to USB in my HeadFi rig, but I’m due to get my DNA 0.5 back from SMcAudio soon with full upgrades and I think hearing it in my 2-channel system will be even more telling and will share those impressions too if anyone is interested. 

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.

I'm using a Sonore Optical Rendu usb to a Sonore Ultra Digital converter which sends i2s out to my Musician Dac. I'm very pleased with the results. 

@soix theres a growing tale that musician has always made Denafrips gear but there was a spat between them and musician decided to release its own line of almost identical gear. You can read about the drama on head-fi 

I recently bought a Sonnet Morpheus with both the USB & i2S modules since I currently have usb out from my Innuos zen, but buying a demo Denafrips Hermes from Rob at Audio Art, so I can use i2S on Morpheus (or AES, but every Morpheus user says i2S is best)

but like you said and I’ll add… outside of the Holo as I’ve not hear one, almost every DAC I’ve heard or knew some preferred AES or i2S. Not one of them thought usb was best. 

Plugged in my Audio GD DI-20HE DDC over the weekend.
Also added a new modded network switch, USB cable, and ethernet cables.

The sound was 'jaw dropping,'
At some stage will evaluate on its own, but as part of a whole, brilliant.