I have been surprisingly happy with the V5i in spite of my mistakes with it. It is a little forward sounding for my taste, yet with certain cans it is a win. So far I have tried the Hi-Fi Man400se and really like what it does with the bass for these cans. Then I tried the Beyer Dynamic DT770 pro which already has great bass and found it to be too much in every dept. The DT are more sensitive too. Never having been one to stand in one place for long, I am now working on the DT770 pro which involves adding detachable cables, and some 'special' padding for the inside of the cups. No idea of how it will turn out yet, as the new cable has just been ordered (Mogami 2592?), but the parts involved for the rest of this cable upgrade are really good. Got the plug from another guy on this site, and it is the best one that I have seen for aftermarket. More later, less sooner.
Can't tell from photo, but are you using an opto coupler here? It doesn't look like it.
Whammy is up and running, kinda. Waiting for the arduino nanos to be delivered so i can re-flash the R2R volume controller and do some cable management.