I've never really had more than one IEM at a time. I usually lose them, then replace them. I usually don't plan ahead, I just roll the dice and find something local I can get quickly. However, I happen to have 4 sets of IEMs at the moment.
I don't know if my perception is normal or perhaps I'm just completely insane, but this is how my brain is working with the IEM's. I've never noticed this at all with my home hi end audio system and I have 2 totally different setups that I would consider hi-end. Dyne/B&W Nautalis.
I own Sennheiser IE8s, Monster Coppers, Monster Golds, and some old Shure 410s.
- When I put in the Sennheiser IE8s for the 1st time after the coppers, they sound fine immediately.
- When I put in the Monster Coppers for the 1st time after the Sennheiser IE8s, they sound small and it seems less pleasant at 1st.
Now here is the kicker. If people would ask me which one I like better, I would say the Coppers every time. I think they just sound much better and are more enjoyable for me. But, not back to back. I think I might be insane, or my brain just accepts the open sound of the IE8s more easily. Anyway, just a weird experience. But it's great having all the different units to enjoy.