Originally Posted by irvin59
As for adjustability, I am not a diy person at all and was scared when I rolled my first opamp-once you get into it though it is really quite easy and lots of fun. It feels like you get a new amp every time, and the differences between the various opamps and different types of biasing can be quite dramatic.
Yep, I can second that. I was pretty reluctant to fiddle around with it, but it is truely worth it. Xin was even kind enough to add another pair of OpAmps to my order for free, kind of a present. With the new V6 it should be even easier to play with it, because you no longer have to be carefull not to break the wires connecting the two boards, you can now "remove the ribbon cables and open up fully the two boards" [quote from Xin's page]. This has been my only concern (besides broken legs of the OpAmps) when rolling the OpAmps.
Its versatility is one reason why I favoured the SM with regard to the SR-71. There are numerous OpAmps one can try and enjoy all their different abilities. With the new V6 there should be even more options.
Another reason were the 4 switches. With my Etys the impedance switch made any P->S conversion cable useless. The bass boost now makes my UE10s more fun when listening to electronica - it's reaaally great.
I don't remember the specs of my V3, but I believe the V6 has a longer battery life.
Nevertheless you should take the two different sound signatures into account, too. As far as I know there's no OpAmp that'll make your SM3 sound like the SR-71, so you won't get both when buying the SM3.
It's basically a decision which kind of sound reproduction you prefer, just the same game when deciding on cans. Though I've only heard the SM3 yet, if one may believe the reviews of the SR-71, you can't go wrong with either one.