If you're interested in the M4U1, you should also take a look at the NAD VISO HP50. They're very similar to the PSB (also being designed by Paul Barton) and are a great pair of headphones. They're basically a slightly less balanced, better build, and IMO better looking M4U1.

Quote: I would say vs the s4, the Rio have more bass, and sharper highs. The s4 also has a bit better instrument separation. But... from what I've found the Rio take to EQing rather well, but it's better to use an actual EQ app, or a dedicated EQ over built in presets with them. As I said...

Well, after a couple days with them. here are my thoughts.    I purchased the Rio's through a groupon deal for $40, and for that price, I really couldn't ask for more, and as a whole, I think they're a pretty solid pair of in ears.  The Rio are definitely bass heavy, but not so much so that...

I have a pair coming, and they should be here tomorrow. I'll report back on what I think of them.

Quote: The Ne-700 get my vote as well 

I had the pleasure of listening to these at the ultrasone booth at the AES expo in San Francisco.  Unfortunately I wasn't able to listen to them for very long, and the ambient noise in the room spoiled the experience a bit.  I was generally impressed, and loved the weight of the phones, but I...