I use stainless steel when possible and it seems to sound better to me imo too. But if you use it for all of your drivers it'll either strongly limit your driver positioning or make your IEM shell huge.
I received the IEC711 from Aihua a few weeks back. This was my previous 7 driver measured with the ESI U22XT sound card. I'd say it sounds more like what I'm hearing from the IEM compared to the Chinese imitation 711.
Composite middle high frequency 31749 BA；
+very high frequency 30095 BA；
+120Ω middle frequency BA；
10MM dynamic driver speaker.
TWFK31749 is a dual driver. WBFK30095 is a single super tweeter. I think 120ohm means that the DC resistance or stated impedance of the mid driver is 120ohm.