I'm currently saving up for the O2 and the ODAC as separate entites from JDS. I want them separate so that i can take the O2 with me to work/ other portability reasons, and when i come home i have a decent Desktop configuration. The only question i have is, when i own just the O2, before i can afford the ODAC, what benefits will i see from taking the O2's input from my soundcard's output? Just output impedance and max power?
There are two other improvements depending on your setup.
1)In Win XP digital volume adjustment meant getting less than 16bits of info other than at max volume. The audio quality can audibly degrade at less than max volume. The O2 lets you set max volume at the laptop and use the O2 to turn the volume down. (The ODAC gives you back digital volume control so long as you set it to 24bit as there are enough bits to endure bit stripping.). It;s been said that Vista corrected this XP flaw.
2)Noise: some kinds of source noise do not increase with increased source volume. If this is the case then by whacking the laptop up to max volume you can get the audio so far away from that background noise that it is inaudible.
One issue with the above is that if you are feeding sensitive phones then even at 2.5x gain you can't get the pot higher than 9pm on the O2 which is in pot channel-imbalance territory (which happens at the lower end) especially if you are a quiet listener. As a loud listener using armatures I am often at 9pm and I believe I may have experienced this issue. It's one reason a lot of O2 users change the 2.5x gain to 1x (ie. no gain).I'm not sure what the situation is with max volume on the source but in some cases it is bound to be too much even for 6pm on the pot.
Possible 3rd: I'm lead to believe that an amp straining to produce current for a low impedance, high-current device can start distorting. I;m not sure that this is true. If so then that extra power will not just give more volume but also avoid distortion in some cases. Perhaps someone can correct that.
Keep in mind also that the Odac requires an amp. So if you haven't already then the O2 is a stunningly good value amp that you'll be needing.
Having said that: the Behringer UCA202 measures well, as done by guess who, and at half the price there's really there's no absolute need for an Odac unless you want the ultimate.(I wanted the ultimate.) It also has the advantage of not (technically) needing an amp. But it does have a very high output impedance so you'll be needing that amp anyway.