I'm using HA INFO Coaxial covertor(16/44) to experience the goodies from "CAS"; want to say that it's worth to begin with...............or start off with any 24/96 convertor to tell your feelings.
I have tested all three DACs under HK$4000 from the bigger manufacturers: Cambridge Audio DACMagic, Musical Fidelity M1DAC, and Arcam rDAC. To be honest, they all suck in different ways. I was expecting a lot more, at least from the M1DAC, but it's disappointing. Having said that, it's already better than DACMagic and rDAC -- these two are so far off that I didn't even bother to consider buying them. (I have tested other cheap DACs as well and you literally have to pay me to take one home.) I did end up buying an M1DAC just because I thought I needed a USB DAC, but it's just the one that sucks less... Everything coming out of it sounds thin and flat, no matter you use USB, optical, or coaxial, connect it to a computer or a CD transport... The problem with these new cheap DACs isn't really about the USB interface, but that they just aren't very well designed/ made... Even funnier when people get all obsessed with this 24/192 thing... It's almost silly... I feel that I'm happier playing 192kbps MP3 files through my computer's onboard optical output to my 20-year-old 1-bit DAC and playing FLAC files via anything to these cheap DACs...
Think I digressed too much... Anyways, if you must buy a new USB DAC under HK$4000, go for the M1DAC... Otherwise, don't buy anything in that price range.