[ADVICE] Dac&Amp for € 500/600

[solderdude]

Acc. to Beyer they are 96dB/mW and at 600 Ohm that would make it 98.2dB/V so I set it at around 100dB/V.
It also depends on how efficiency is determined.
With noise in a certain bandwidth, at 500Hz or at 1000Hz.
Then there is product variance as well as well as measurement error (calibration).
Differences of a few dB are not uncommon.

 

[intelfx]

I'll have to jump in — nobody replied to my question in the DX7Pro comments section. Let's say I have the DT990 600Ω and DX7Pro (built-in amp). According to its specs it is rated for 300Ω on the unbalanced output, and 600Ω on the balanced one. According to measurements here on ASR, its unbalanced output can deliver ~120mW @ 300Ω.

I attempted to test-drive the DAC/Amp with 250Ω and 600Ω variants of the DT990, and I think the 600Ω variant sounds worse. On the resident demo amp though, I liked the 600Ωs more. (but it was not a blind test and I'm not in any way an experienced listener, so it may be a case of confirmation bias — or confirmation bias that I have confirmation bias?)

Does that sound plausible? If yes, then will I benefit from rewiring the headphones to use a balanced connection? Or should I get a better amp? Or should I get 250Ω headphones?