I received my M5's at work on the 6th (thanks, Road-Dog!), opened them when I got home, played pink noise through them for a couple of hours only, then couldn't wait to try them out.
Either they're not as big as they look in photos, or my ears are bigger than I thought they were. I haven't liked other flanges, and these were no exception, so I tried the two sizes of foamies that came in the packaging. Worn with the cords up and over my ears and with the larger foamies, they conveyed a lot of bass ... and nice detail. Right off the bat, I found them fun to listen to ... with a big, full sound, and noticeable separation of instruments.
My ears and ear canals must be different from each other, though, and after the ultra-minimalist presence of the tiny ER6i's with short Comply foams, these seemed potentially uncomfortable in and on one of my ears (it even seemed like they were too small for me to wear them with the wires over the ears, which surprised me). So I tried the smaller foams, again running the cords over my ears, and this felt more comfortable, at the cost of some of the big bass presence (as with any in-ear 'phone, bass seems dependent on filling the ear canal just so).
I ended the "try-out" session settling on the large foamies, but with the wires worn "down." The M5's looked surprisingly like larger versions of regular canal phones such as the Creatives or Sennheisers. Not as weird looking as I was led to believe, worn either way, but certainly no beauty contest winners. But they sound ... really nice ... really impressive even before full burn-in. I listened using an EQ'd Rio Carbon (very large bass presence) and a flat iPod Nano 2nd generation (even this sounded richer and fuller with the M5's than it usually does). I look forward to trying more combinations (Comply and Shure foamies, a PCDP, smaller flash players, Rio Karma, etc.).
I think I would need medium Shure foams or regular Comply foams with these (with the ER6i's, the body of the earphone and the short foam both fit into my ear canal; with these, only the ear tips "project" into the canal, and to get the fullest sound, they should fill the canal as much as possible).
After all my slight upgrades, sidegrades and backtracking, I can recommend these as a very worthwhile upgrade from standard earbuds and from canal phones, as well. Very, very good bang for the buck. They might not please some name-brand-conscious consumers, perhaps, because they aren't sold in the Apple Store and they do look a bit geeky, but that would be their loss.
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Phones (in order of purchase):
Sony MDR71, Sony MDR51, Etymotic ER6, Panasonic RP-HJ50, Shure E3C, Koss PortaPro 2, Creative EP630, Etymotic ER6i, Sennheiser PX-100, Sennheiser HD555, Future Sonics Atrio M5
Sources (in order of purchase):
2nd Generation 10GB iPod for Windows (retired)
Creative Muvo 256MB
Creative Muvo 1GB (out on loan)
Rio Carbon 5GB
Cowon iAudio 5 1GB (out on loan)
Rio Karma 20GB (low-mileage collector’s item)
Creative Zen Nano 1GB
Samsung YP-U2 512MB
4th Generation 40GB iPod (monochrome; used as home jukebox)
2nd Generation iPod Nano 4GB
Creative Zen Stone 1GB
iRiver T60 2GB