I've been using the ZDAC for 5 months and I like it alot. Very smooth sounding and little digital glare. I've tried a bunch of USB cables from my computer and settled on the Cardas Clear which is a good match. I tried the Black Cat 75 ohm spdif and was wonderfully detailed but lacked density and was just too analytical for me. Also tried toslink from my Creative ZXR daughtercard via the Van den hul Optocoupler and still preferred the USB port even though it's max is 24 bit 96khz. I tried ASIO with the ZXR/ toslink with JRiver 19 and kept losing the signal so went back to USB WASAPI. One thing I found is that the ZDAC needs an upgraded power cord. The Pangea made a small but noticeable difference, Venom 3 was similar, especially in the midrange. Then I took my Cardas Clear from my reference system and tried it and I was not prepared for the staggering difference that made. Holy crap it is delightful! But a $750 power cord on a $475 DAC is not something everyone could try. If you do not believe that power cords make a difference, please do not comment as I don't want to hear it because I AM hearing it right now. Amazing. Then last month I got the HE-500 cans with Q Audio French Silk cable, changed my wall outlet to a Maestro, and used a Cardas 1/4" to 1/8" adapter since the ZDAC only has a 1/8" headphone plug. After a 10 day break in I was really impressed with the dynamic, clear sound but felt something was still lacking so I ran a 1/2 m Audience AU24SE interconnect from the ZDAC to my new Schiit LYR headphone amp with the Venom 3 power cord. Now things are getting interesting! Then last week I rolled the tubes to NOS Siemens 6922's and am finally getting the transparency and dynamics for which the HE-500's are so famous. Diana Krall never sounded better and The Tord Gustaven Trio sounds incredible. I am a long-time analogue buff and I can state that this is real high-end sound now. Of course I will keep tweaking and might get a more expensive DAC to complete the setup but for now I am in audio bliss. BTW the ZDAC has Asynchronous sample rate conversion for all inputs including the USB input.
That's interesting that you did indeed hear an improvement with the Zdac once you upgraded the power cable. The stock cable that came with my Zdac is still in the box as I never tried it, I already had a nice power cable form Audio Art in place for my Benchmark DAC1 so I used it for the Zdac. I guess its possible that this is the reason why I've always heard the improvement of deeper, tighter bass with this DAC without it ever sounding as if its losing control in the bass region...who knows? I do know that the Velodyne DD-10 is powerful yet tight "IF" the signal feed to it is as well...feed it loose, out of control bass and you won't be pleased with the results.
I'm fortunate that a very good friend of mine got into this hobby years ago at about the same time I did and this has allowed us to swap gear back and forth between our two homes and this way we're able to try out twice as much gear as we'd be able to on my own. We've done this going all the way back to the early 90's when Apogee Speakers were getting a ton of attention for their line of ribbon speakers and Infinity Kappa speakers were very popular. Back then, at one point we both owned a pair of Infinity Kappa 8's (with the incredible for its time EMIT tweeter) and later moved on to the Apogee Stage. We both bought so many amps, trying to find just the right one and back then it wasn't easy finding a solid state amp that didn't sound too dry, brittle at the top end. I think we started with the extremely popular Adcom GFA-555 and then the 555 MKII and later moved on to Nelson Pass designed Nakamichi PA-7 Stasis amp and a year or so later I ended up with Mondial designed Aragon 8008. This was before DAC's and I remember having so many mods done on different CD players that looking back it was ridiculous...we're so lucky now in that there is a TON of great sounding gear available and regardless of the price point there's truly no one right answer, be it for speakers, headphones, amps or DAC's.
There are probably half a dozen DAC's under a $1000 right now that I would be more than pleased to own and with lower priced digital getting so good and advancements being made so often (so it seems) "I now try" to stay under a $1000 with my DAC's be it for my home or office system. I'm very pleased with the Zdac, yet I could easily live with thoroughly enjoy the Schiit Audio Bifrost with the available upgrades (I LOVE their Lyr HP amp) or several other high quality lower priced DAC's. Changing gear all the time can be a blast yet after a while if you're not careful it can become maddening...you can lose sight of the main goal and that is to enjoy music. I truly think the key is to find the gear that YOU enjoy most and then try very, very hard to forget about the components that you've put together and get back to focusing on the music.