Beyerdynamic A2 at 100 ohm output imedance with +6 decibels has tightened base and mids of Beyerdynamic T1 2nd generation. It also put adequate control on treble which finally sounds normal. I've used T1 with Arcam rHead which did not have problems in pushing T1 to the highest level, but it did...

arcam rhead worked perfectly with SRH-940 and SRH-1540 that have lower impedance, but had loose bass with Beyerdynamic T1 (2nd generation) and their 600 ohm. I guess high imedance T1 (2nd gen) headphones requires high output impedance which is not there with rhead.