The transducer will ALWAYS make the largestt difference, for better or worse. In loudspeaker audio, the rule of thumb was that you should invest haf of your budget into the speakers and the other half into source and amplification. The same or similar holds true in head-fi...perhaps not half, but the cans should be the 'best' portion of your chain. For example, if you have $2,000 to spend...a pretty large initial budget...I would recommend $900-1000 cans and $900-1000 of electronics to drive it, rather than buying $500 'phones and $1500 on the DAC & amp.
While I have not been the most vocal supporter of he sonic signature of the 10SE, what its price does is allow you to invest more in the phones than you could have otherwise while keeping to the budget.
In short, I'd rather see someone buy LCD-2's and a 10se than a maxed Woo WA6SE to drive Senn HD-25's for roughly the same budget. Always dedicate the most you can to the transducer.