I actually find the synergy of the CLAS and SR7-B to be spot on. A very balanced sound delivering detail, punch, drive and emotion. You will hear a great many people say this amp is dark, in fact I was with a fellow headfier on Saturday who has made this comments before. He listened to my rig together with LCD2's and my Final Audio Design Piano Forte IX's.
He could not understand why the amp did not sound dark, just clear and musically very involving. My theory is that a great many here review product without having that product for a great deal of time. I have had my amp now in use for over a thousand hours and I think that is the thing. I found this amp really came on song around the 500 hour mark and levelled off at around 700 hours.
I compared whilst at the meet to the Tube Schiit amp (can't remember it's name) and that amp, which was a product display amp with a lot of hours was not in the same league as the SR71-B, it was harsh, un-musical and just plain boring. Also, to note. The other piece of trot handed out here, that the blackbird is not as good from the single ended output. All this listening was done from that "poorer" output!
Also, don't confuse a brighter more trebly amp with clarity, it is just more tiring over longer listening periods. There is no detail lost with the blackbird, no rolled off high's just a balanced, well thought out mature sound that one can listen to for literally hours on end with no fatigue.
The difference between balanced and single ended output is not as huge as people make out here and is very dependent on what headphones your listening to. IEM's or easy to drive full sized the difference is small or non existent in my experience. Also, it will drive very well the likes of the HE-500 and make a good job of the HE-6 though it has to be said they do sound better with a more powerful amp, but out of the blackbird the sound would make you happy.
Remember one of the things of this forum that really bugs me is that anything over six months old is old hat and suddenly sounds terrible compared to the new stuff, the same reviewers six months previous raving about the old stuff. Just go through the so called "golden" reviewers here and see what I mean.
I have found one of the few who does not do this but sadly no longer reviews portable amps is skylab
Now, take my thoughts and understand they are just my perspective but I encourage you to read others and come to a balanced choice. This stuff is highly personal remember. Also, something that measures well does not necessarily mean it will sound good!
The other thing to remember when taking peoples opinions here is what they listen to, what bit rates and what their hearing is like. You will find in my profile the type of music i listen to and below the equipment I use. I just had my hearing checked so will add that to my signature. I say this as someone may say the treble is rolled off but can't hear past 17KHZ. To my knowledge the only other person who states their hearing capability here and is another of whom I trust a great deal is James444 from Vienna.