Well. Today was interesting.
I had a friend round to listen to my O2 amp. He bought his iPhone 6 with him so I was able to give it a listen.
I really liked it.
Against my 5S it seemed to be a step back toward the less digital sound of the 4S.
With added weight and clarity.
The differences between the 6and the 5S were subtle but significant. IMO.
My friend is blind. So a literal blind test!
I switched between the two phones on HO and he consistently preferred the 6. Interestingly he found little difference in the bass but more in midrange and treble.
He also thought the soundstage was wider.
I didn't hear those differences but definitely preferred the bass of the 6.
All listening was done with the Sennheiser HD 600's.
Neither of us detected any difference in volume between the two phones.
Both running at maximum to drive the 600's.
Incidentally. The O2 simply added volume and did not change the SQ.
As I expected.
I tried the 6 with my IE8's and was surprised to find that the 6 suited them very well. Adding sub bass without exacerbating the midbass hump.
Volume from the HO was more than sufficient.
Basically, I cannot wait for the 6S