Ok, a few 602 impressions.
Testing is 602 HO --> D7000 versus QA350 HO --> D7000. Both units running for 30 minutes using WAV files of Roisin Murphy ('Let Me Know' and 'You Know Me Better') and Harry Nilsson ('One' and 'Remember'). Both units batteries at 50% or less at start of testing.
Quick notes. Using the QA350 which uses a single Wolfson 8740 compared to the dual DACs on the Sflo2 but by all accounts the QA350 is the better performer but not by far. Not sure but the Sflo2 might have had a slightly wider SS but it is no longer in my possession to verify. Did my best to match gains. About 5.75 volume, high gain on 602 and about 5 dots @ 10 'o clock on QA350. Both sound great on the D7000 without an amp and produce plenty of volume. I do prefer LO to Arrow though in both occasions. Definitely not a deal breaking night/day difference. Not so sure about that after going back to the LO anymore.
The best analogy I could make between the 602 and the QA350 is that of digital versus analog which has been said repeatedly already. A good headphone reference would be the M50 versus the HFI580. The M50 sounds more natural and organic whereas the HFI580 has a bit of that Ultrasone unnatural timbre to it. I don't find it objectionable but it is noticeable by comparison. It certainly can be useful for electronic based music. Another is the use of edge enhancement on HDTVs. The idea behind this technology was to sharpen the edges of screen images to give the consumer a better impression of detail and sharpness. The problem is that it often looks unnatural and creates odd anomalies which is why most video purists have it disabled on their High-end screens. This is exactly what I hear switching between the 602 and QA350. At first listen, if you are used to that more digital sound details jump out at you, separation appears clearer and sharper. Switching to the 602 then sounds less bright, less sharp, it has a bit more noise but not as much as other players I couldn't stand for more than 2 minutes. So the QA350 does appear to offer a blacker background on which to paint its sonic picture. But is the 602 less detailed? No, everything you hear on the QA350 is resolved clearly and to my ears in better fashion. This becomes apparent switching back to the QA350. Female vocals sound more unnatural, brighter and more processed than the 602 which has a natural smoothness to vocal qualities. Treble has a sort of harsh, brittle quality to it on the QA350. String plucks and cymbals sound a bit too metallic. Music just sounds more natural and flows better to my ears on the 602. It becomes very engaging and sucks you in. By comparison now the QA350 gets more fatiguing but is still an enjoyable listen once you acclimate. It just sounds less refined compared to what music sounds like in a live setting. The QA350 just sounds like everything that should be there is there but a bit exaggerated. A bit too much bite here, a bit too much reverb there and slightly too bright. At times the 602 can be somewhat fuzzy and congested in comparison though. If the 602 is like water flowing along a creek bed, the QA350 is like the crack of lightning striking the ground.
As to the earlier Bass rolloff in my discussion w/ yoos. I still think the 602 is slighty rolled in comparison but I seem to notice adjusting gain higher on the 602, bass seems to get bigger compared to a more linear response on the QA350. I could be wrong. Who has the better HO? It will really come down to signature preference. As to which is truer to the source? That's a very complicated question for another thread. Which is more detailed? Depends on how you perceive the picture being painted. YMMV.
Update - Ahhh, so much better now LO --> Arrow (Bass 'O', Imp 'O', Xfeed 'O', Gain 'II'). Less congested, more separation and better SS and imaging. Details galore, no need to search for anything. I wasn't able to notice much difference HO v. LO a week ago. Now that I've had more time w/ the HO I hear the differences. HO compared to HO I can understand anyone preferring the QA350 or 602 over the other. Most would go for the QA350 signature. But amped via LO it reminds me clearly why I sold my Sflo2. I'll take my 602 amped over the QA350 amped. The QA350 sounds muddier and less refined than the 602 clearly. The Sflo2 performed less well than the QA350 LO last I compared. The 602 is another level of performance IMO. Everything just sounds 'right' now.
I might update comparisons later using my ESP950.
But it is very picky regarding cards.