I would like to state further-I had at the time Theta's pro basic2.(2K)The Quantum (3.4K) dac was on par with 'IT'.I kept the Rez.dac for about 3 weeks.I finally exchanged it for Gen5/+(450.00), before the a mod came out.Brand new with 2 day's breakin ;sorry,not even close.So I repeat giant killer,my FOOT. Don't believe all you read.How this compares to the new 50/55 ? - never heard them. There was a reason Theta got an A rating,and a reason the Quantum got a B.But one should always listen at home yourself. The used price reflects the differences.