I've got it on my desk right now. Incredible how low the noise floor is from USB from a notebook computer. You can use this when your notebook is on battery power and get ultra low noise. The amp has a very unique sound signature which has to be intentional. It seems biased towards the mid to high mids with very very low emphasis on bass and highs when powered by USB. I've not tried it from a wall wart USB or with a proper power supply from the mains.
There are indeed two headphone outputs, both powered by OPA 552 burr brown chips.
As for Bass and Treble controls - they are intense. Without them there is significant bass roll off at least from USB power and some treble roll off, too. The result is a ringing, energetic high midrange that has a 'live' sound, much more like being at a concert than being at home. It is disconcerting at first, but after a few minutes, fun, and hard to change away from. Now, dial up the bass dial and the effect is as intense as the Vorzüge VorzAMPduo which is simply incredible.
I've only listened to trance so far with the HA-02, but I like it very much. Remember, I am a firm believer in a sense of space and that space is built often in higher midrange where ring and clanging sounds erupt. I've got no idea of the control the HA-02 has or how it really works with earphones yet, but I can say this: of all desktop amps I've used, it has one of the lowest noise floors (in terms of background noise). I doubt Fischer were aiming at anything but fun in the designing of the HA-02, and they seem to have hit their mark.
I didn't think anything when I saw it in product catalogues, but today, after a first listen, I'm thinking that it may be a great pice to add to my fun kit. Again, bass and treble controls are wonderful and have immediate, profound effect and still, even when engaged, the noise floor stays very low. Impressed but perplexed am I. More impressed though, as it is another evidence that amp makers are designing sound rather than just making devices that sound 100% like the original signal. I'm a fan.
I may even decide to do a review of it rather than just take product photos of it.
EDIT: I should mention that at 100% volume with Audio Technica ES10 and driven from USB, there is little to no sizzle in the signal, but it is far far too loud for human ears. The Fischer Audio FA-002 exhibits NO sizzle whatsoever at 100% volume. Only with bass dial engaged does sizzle come out. At about 80% of the bass dial, any headphone attached exhibits 'diffraction' where apparent resolution of bass is smeared while the overall quantity is increased. Apart from that (not that that matters as otherwise, performance is excellent in bass/treble dials), there are few anomalies that don't seem to be programmed into the HA-02.