Which DAC is better?

Yea, the conversion to a computer-based source can be daunting at first, but if you're inclined to keep at it, it will be old hat in no time.

My first-hand experience with different DACs is somewhat limited. Have an Ayre and an MHDT Havana. They are very different animals. The MHDT is a non-oversampling (“NOS”) DAC. That is, it uses cost no object DAC chips from, say, 20 years ago with a USB (and other) inputs. If all of your source material is standard CD (the standard is called “redbook” and is encoded with a 16 bit word length and sampled 44 thousand times per second, which is what 16/44 represents) then a NOS DAC makes some sense. In effect, it’s chips address all redbook material in native resolution because, you guessed it, the best chips from the hey-day of CD ran only 16/44. (Or, at least that’s my imperfect understanding – the Ayre doesn’t “upsample” either, but will run high-rez up to 24/192, while the Havana will not…). But if you want to run any higher-rez material or upsample, one of the DACs running these old-school chips isn’t your answer. Personally, prefer the Ayre, but there are those who don’t. Also liked the Bel Canto, which is actually not a USB DAC, although it does have multiple inputs and a volume control, so can function as a stand-alone preamp as well. To run USB into the Bel Canto, you need a separate Bel Canto converter ($500). Sounds great, and a fine non-asynchronous USB solution. I went with the Ayre.

Otherwise, the original (pioneer, really, I believe) of asynchronous USB is Wavelength Audio. They do multiple iterations of tubed DACs that are meant to be very nice. For years, Wavelength was the only game in town for asynchronous, and everyone else was either working on different technological answers to jitter in an off board DAC, decrying USB DACs as inferior, or waiting it out. Ayre, for it’s part, licensed Wavelength’s asynchronous tech, and thus became the first (and for a spell, I believe only) solid state asynchronous USB DAC on the market. Think it was these two that really opened up the market, and since then there has been a real explosion of asynchronous USB DACs (presumably using iterations of the basic technology to do the same thing). These days, seems that asynchronous is the prevailing way to go with USB to a DAC, but there are many that offer different solutions as well (i.e., the Bel Canto or the Simaudio). Everyone, from “The Names” to newcomers seems to be getting in on the act, so there are lots of options.

As for what’s caught my eye – and admitting that I have no first-hand experience – been interested in the offerings from the likes of Naim, ARC DAC 8, and recently seen some good feedback on the Rotel. The Benchmark DAC-1 is another, and one that seems to be very polarizing (it is from an established pro audio shop that has made a big crossover, and folks seem either to love it or hate it). More recent-ish additions, the offering from Empirical Audio (which is very active on these forums) looks interesting, and a lot of good feedback regarding the Wyred4Sound DACs. I’d love to hear all of these, but haven’t had the chance. So, lots and lots (and many more) to choose from. Best of luck and enjoy.

Gosh, "super USB", well that must be the best...

There's no such thing as super USB.

The Ayre and the Arcam will accept both USB 1.1 and USB 2.0. USB 1.1, otherwise misleadingly known as "full speed" USB, will allow you to run up to 24/96 source material. Above that, it simply will not pass the bandwidth required.

So, to run higher sample rates (e.g., 24/176, 24/192), you need to use the newer USB 2.0 (which permits 40x the data as USB 1.1). The Ayre and the Arcam units support this (although your computer may not), but the Simaudio does not. In fact, the Simaudio states that its USB input will accept ONLY up to 16/48. If you want anything more than that, you need to convert the USB to some other digital format through an offboard converter, and then use that input into the Simaudio. Hence, while the Simaudio provides the capacity to run high def material, it will not accept it over USB....

Otherwise, if it matters, the flexibility of the Arcam and the Simaudio are greater than the Ayre. That is, they both have multiple digital inputs, accepting multiple formats. The Ayre has a single USB only – it is a 100% dedicated, single-purpose USB DAC. Thus, if you want to run anything other than USB, or more than one digital source, the Ayre aint the one for you. Looks like none of them have volume control, if that matters. Also, from the literature, looks like the Simaudio will upsample internally. I know that the Ayre does not, and it looks like the Arcam doesn't either. The Arcam and the Ayre run asynchronous USB, while the Simaudio appears to address jitter through a "proprietary digital clocking system." Asynchronous USB is, by many, considered to be the best option these days. So, the feature set for each is different. The Arcam and the Ayre appear to offer state-of-the-art functionality over USB. The Simaudio does not. In fact, from the technical data, suggests that USB on the Simaudio may have been somewhat of an afterthought.

Sound-wise, that's up to you. Have an Ayre, and it sounds great. But no experience with the other two, so can't really say. There are also many, many other options in that general price range. I suspect that a search regarding USB DACs will give you more suggestions than you could possibly want.