I started looking into asynchronous USB-SPDIF converters after I came across the Musiland 01 device. I'd heard asynchronous USB was a superior protocol for audio as it uses a local crystal to generate the timing, rather than relying on the PC's clock timing. Unfortunately, asynchronous USB audio devices were rather few in number, and expensive also. Then the Musiland came along. I bought one, liked its sound. (compared to the sound of the analogue out from my computers this sounded cleaner with a lot more detail - see below) & started to look at the design.
It did indeed use it's own on-board clock as the master timer for the audio play-out, which was great! On the other hand, it had only a single oscillator to deal with all the audio stream speeds from 44.1KHz to 192KHz. This means only one frequency can have really low jitter, all the other speeds have to be derived by some complex processing. There are two speed 'families' in audio, the 44.1khz family (all its relatives are multiples: 88.2KHz, 176.4KHz) & the 48kHz family (together with 96kHz and 192KHz). For lowest jitter, two different clocks are needed - one for each family. I couldn't do anything about this but there were other areas I found I could address. The power to the clock oscillator was derived from USB power and the on-board DAC needed some work.
Here’s what I said about the sound at the time after my modifications:
"Bass is much more solid & powerful, mids & highs are more crystalline. What I use for listening is Herbie Hancock's River (The Joni Letters) recorded in WAV to disk from CD. As I said before, I'm using a modded Lepai amp (Tripath TA2020) with no caps on the input (because I'm using a transformer). So no caps from DAC o/p straight through to amp input.
My test is to get the brush strokes on the cymbals to sound like brush strokes on cymbals with texture, etc rather than a haze of sound - this gets me closer to it with some texture showing through, not all the way. I haven't heard a system yet that renders this properly so maybe it's in the recording. As for the rest of the album, the voices sound amazingly lifelike (Tina Turner, Corrine Bailey Rae, Leonard Cohen, Joni herself, etc), the piano sounds perfect, Wayne Shorter's sax playing is a wonder on this album too & you can just about hear the spit in the mouthpiece"