I guess I'm weird, I actually tend to prefer IEM's over full-sized headphones. A pair or two of full-sized phones are nice to have around for variety but I'll take a good pair of IEM's any day.
Again, I'm a bit weird. I prefer as little bulk when I'm out and about as possible so I only tend to use my iPhone 4S for portable listening, a DAP like the DX100 would just be something more I'd have to carry. Honestly though, I don't tend to do much "on the go" listening anyway, for me, the HiFi-M8 will mainly allow more flexibility to listen with a high quality setup in different spaces around the house and at work. That does mean that in my situation the Tzar 350 likely wouldn't get used for out and about portable situations so having it cabled with a 4 pin balanced XLR connector wouldn't be a big deal.