I notice slight increases in dynamics (sq) going from mid to high gain (8 to 12vrms) on my kann cube so I would say no
not to their full potential anyway... one thing that I can’t really get my head around is how difficult these are to drive to their full potential.
I think the IER-Z1R scale really well. IMO, they sound good with even an iphone and the Apple Lightening to 3.5mm connector, As you improve the source, the IER responds with even better sound. In the end we all have to just draw our own line cost-wise with these IER, regarding the source.
My Source/SQ experience with the EIR:
Tier 1:
Good: Iphone with lightening cable
A little better: Ipad Pro with $12 usb-c to 3.5mm connector
Tier 2:
Pretty Darn Nice: Ipad Pro with $50 Meizu Pro (Usb-c) Dac/dongle
Very Good: RME ADI-2 Dac/amp
Very Good: Sony ZH1ES Dac/amp
Tier 3:
Incredible: RME ADI-2 Dac -> GSX Mini amp
Drop the mic: Yggdrasil -> GSX Mini amp
I know the above classifications are vague. In short, as the source got cleaner you could hear more and more separation of the instruments, and the highs had more sparkle, cymbal decay was more accurate. And as the EIR had access to more power, the music had more attack, the bass was clean and tighter. The soundstage opened up and the tonal range had less congestion.
In short, the EIR are enjoyable with many sources and you don't need to spend a ton of money, or have the best source ever. My new mobile and office setup is now the EIR with ipad Pro -$50 Meizu Pro dac/dongle. The sound is very enjoyable and the Meizu dongle goes in the case with the EIR. I have my ipad at work and on trips so that is no extra burden.