So, comparing my new IEMs, I have to say that the one that's been impressing me the most is the Denon C400. It may not be my usual sound signature: the bass is pretty subdued and the (brighter) mids are what's taking its place. I don't even know why I purchased these IEMs, but I definitely know why I'm keeping them. Voices and instruments sound so damned clear, yet unintrusive, and just... simply put: adorable. I don't know how to write impressions on these to be honest, they kind of caught me off-guard and they're just so damned good imo. As for sound distortion at higher volumes, I think maybe Denon has a poor QC (or stepped it up a notch) because mine don't distort until I go up to unlistenable levels -- and I have hearing loss. Meaning that I don't get distortion even at loud listening. I'm thinking that I either got lucky with my pair or Denon stepped their QC up.
As for C300, yeah, I think I finally got a fit with them and it was with the Complys. I don't like the Complys, they subdue treble too much, making the sound too dark and somewhat muffled. If I use the small silicone tips I get a fit too, with the caveat the IEMs don't sit securely in my ears (they are huge). They are competent IEMs for sure, with a great sound, however, the fit issues I have with them is pretty bad. The Complys take care of everything, but kills the treble a little. I have hopes that maybe my foams for my IE80's fit these and gives the treble and upper mids a needed boost. Once again, it's hard to give impressions on them because while they sound good, I can't use them, and when I can use them, they don't sound as good.
The Sonys, yeah, they're in a league of their own. They are catered towards serious bassheads, and that's what they do. I got nothing more to say, really. All that other stuff, aside from the bass, isn't bad either. These won't be your standard audiophile IEMs, so to say, but they are good enough for the kind of music that's more reliant upon a massive bass rather than anything else.