this is his first set up, most of us started with the E17, no reason to buy something nicer and then drive it out of an on board pc card that's honestly going to waste what ever headphone he's got. Headphones like the DT 770 LE, the HP 100, the Audio TEchnica ATH A900x and UE 6000 all of which fall into his price range new, are great starter headphones. ANd the E17 is going to give hime him a dac and amp of which will benifit his headphone. Not to mention the E17 eq controls to fine tune what ever he buys.
Let's assume he get's only an K545, and has the fit issues with it, then he's going to have a rather sour sounding headphone.
going un amped with a on board dac is going to cripple what ever he buys. The E17 is so popular because it's such a great starting point for many new members. ANd most of those $300 new msrp headphones are going to be on par or below a $200 msrp out of the E17.
I went through a good number of $200-$300 mid fi headphones my self, and found most all of them to be in the same level of quality. Each had differeing sound signitures, and equal trade offs.
ADditionally I don't think you;ve even heard the K545 have you Money? DOn't recommend gear you've never heard your self. I've listened to all of my recommendations, I have a review posted of them all on head fi around here some where as well.
I've found it's best to start with introduction gear, like the E17 and a nice Mid Range can in teh $200-$300 [used at $300] bracket then jump straight into a headphone like a Mad Dog [which needs an amp honestly the E17 might not suffice...] Start small and work you way up as your feel comfortable, if your only listening is with Apple Ear Buds, you may not appreciate or even notice the differeances between a HE 400 and a Dt 990, The HE 400 costing twice as much as teh DT 990, for example. Things like Sound Stage & 3D image, speed and decay are the biggest features of upgraded headphone, and going back to the HE 400 and DT 990, I owned both and found the HE 400 was only better than the DT 990 once I dropped $200 into it, with a Recable and new ePads. Not to mention going with a balanced amp, after dropping a LOT of money into my Source and my amp, only then did the HE 400 come out cleary aheaded of the DT 990, how ever stock He 400 and stock DT 990 out of my old mStage... they seemed to b more on the same level and again my dt 990 pro was $150 new, my HE 400 $300 used.
But, op it's up to you. I highly recommend you start off with a low priced headphone, something around the $200 msrp new. Beyer, Audio Technica, Akg, Sound Magic and Logitech along with Koss and Sony are good brands to look into, with an E17 and a well recommended headphone from the $200 bracket, I know you'll be happy, additionally when you upgrade to a nicer headphone, the existing Dac and amp in the E17 should allow you to better enjoy the upgrade.