The iPhone will drive the headphone fine and make a very nice sound, but the amp will make a big improvement in harmonic extension and soundstage. Use the amp whenever possible. Both Headfonia and I concur that the E07k is a great amp, and probably the best thing you can get for up to twice the price. I’m familiar only with the E07k, the E17, and the E12. I think the E07k beats the E17 (and both are also USB DACs), while the E12 is just an amp, and has a darker sound but with more power for inefficient headphones. The Philips is not inefficient.
One thing I suggest to prospective customers for a specific headphone, if I have that headphone on hand, is for them to suggest 2 or 3 music tracks by a particular artist and composer that I can sample on that headphone, not so much for me to suggest how it sounds, but mostly to check if that headphone has any real sonic issues with that music. For example, a headphone that’s ideal for classical and acoustic music might sound too harsh with metal and industrial goth.
There’s a lot of debate in the headphone world about wireless audio. Wireless standards like Bluetooth are capable of making music sound great, but because Bluetooth relies on data compression, it will never sound quite as good as a wired connection. The big question is, with the improvements in Bluetooth, can anyone tell the difference anymore between Bluetooth audio and wired audio? We’re skeptical that the difference is meaningful, so here’s our best advice: if you’re an audiophile who cares about hearing music in high fidelity, you’ll probably be better off with a set of wired headphones; if you need everything to sound great but prefer the convenience of wireless connections, go for a pair of Bluetooth headphones.
In-ear headphones are like earbuds but are an upgrade to them. These headphones fit into the wearer's ear canal and stay in place with the use of foam or rubber tips. These tips are available in custom sizes so they can fit each individual wearer. When a proper fit's achieved, in-ear headphones reduce outside noise and deliver sound quality at about the same level as over-ear and on-ear headphones.