Ryan,
I've tried them multiple times now, both stock and modded and have yet to find a good reason to own them over the Senn 650s (or 600s for that matter). That's not to say that I don't think they're on par with the Senns, I'd actually say in terms of relative fidelity (accuracy, neutrality, etc.) that they are similar in terms of overall performance I just happen to prefer the Senns in every rig I've tried them in. Like a lot of things it's going to come down to whether or not they're your cup of tea and fit well in your rig.
As far as amplification is concerned you're going to want something with boat loads of current and voltage gain. My PPA V2 w/ a gain of 8 wasn't up to the task w/ a 1V source. The Wheatfield HA-2 w/ the Hertsens was a lot better and pushed me to the edge of keeping the K340s. Ultimately though my interest in them waned and I decided to try something else (the failed W5000 experiment).
And depending on the FOTMness prices can make them very unattractive. There was a time when stock pairs were going for ~$300 (for anything in a condition that I'd buy anyway) which is at least $100 more than I'd pay for them. Larry's mods aren't cheap either so be sure to factor that into whether or not you want to make a run at them. At a minimum you're looking at ~$275 and I personally would want a 3 meter cable, why he even offers a 1m length is beyond me. Like you're going to use these portably and have an amp in your shirt pocket...
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