Have you sent the AZ70 back yet? If not they just released a new update for the IEM and it changes the sound quite a bit I think. Can you apply the update and give your new impressions before you send them back?
I went through each of the songs after firmware update on Technics AZ70. The tough part is that I have no way to A/B test with & without update. I can only go by my recollection of pre-update to the best of my abilities without knowing what was changed & what wasn’t.
Carmina Burina (o fortuna) - Bass is still not as powerful as cx400bt. Soundstage is still lacking.
Next up "Concerning Hobbits" - Mids are probably about the same. Highs are still awesome - I can't really tell with this song if they were toned down. I do prefer the Senns for highs because they are bit more detailed & rich.
For vocals going high - I listened to Journey's 'Don't Stop Believing'. Very clear highs without distortion. There is no way you would not enjoy this AZ70's sound signature - it's fun and clear. Senns are just a tiny bit better.
Heart of Courage - AZ70 still missing that 'oomph' that Senns have in the bass region. Highs are nice. Soundstage still not quite like the Senns. Great detail - you can hear all of the instruments and differentiate them individually in Heart of Courage & O fortuna. Sennheiser has a minor advantage in details though - it's definitely noticeable if you do A/B testing.
'Clarity' by Zedd - Soundstage is still bit lacking relative to Senns. It is most observable when the music opens up in stretches. Vocals are clear. Highs might be bit tweaked here - I think you might be right, they may have toned it down a bit. I didn't think they needed to tbh. If they did, they probably did it to make bass stand out a bit, which might be a smart calculated change (I'm guessing without knowing for certain).
Beethoven’s Fur Elise - All piano. I would say it’s lots of mids, maybe with some highs. I felt it sounded just as good as before. I don’t know if frequency changed between updates. If update softened up treble frequencies a bit, it’s difficult to tell with 100% certainty without doing A/B testing.
Ran through 'Chariots of Fire' theme song and 'Conquest of Paradise' both by Vangelis. I don't have enough knowledge about music, but I can tell you the two songs have very different tones and pitches. Chariots of Fire is a musical with open style tone, which is good for soundstage test. I find it sounding good, certainly good enough for anyone, but Senns just have better stage depth tbh (sounds more open like being in an auditorium & more "spacey"). Conquest of Paradise is very different - it's bass deep vocals but with some background violins/other instruments that go high in notes & piano mids. Bass, well you know my thoughts on AZ70s bass strength by now
Sennheiser cx400bt just has better overall sound. Technics AZ70 is close behind and good enough for anyone, but Senns have a slight advantage (significant advantage in lows & soundstage imo but the rest is close enough that it doesn’t matter all that much unless if you are stubbornly audiophilic). This is my first experience with earbuds so unfortunately I can’t compare it to anything else. I mean I have the HD600 and DT880 to compare to, but that’s not a very fair comparison to make, is it?
