Advice on nice sounding portable setup

Hi guys, need some advice on a new setup please.

I'm a trained sound/mastering engineer and at home I have my iMac running through an Apogee soundcard into a pair of Focal CMS 65s.  Sounds lovely, the monitors are amazing and the Apogee brings such a wide and detailed soundstage!  I often use it just with my phones, Beyerdynamics DT250s, and it's just as good.

At the moment for portable, I have an iphone and an A-series Walkman, both sound OK for portable gear, but nothing close to my home setup through phones, the difference in clarity is night and day through the same phones.

I'd like to know if I can get anywhere close to the quality of sound on my home setup, with a portable setup?  I'm not going to change my phones as I've had them 10 years and I love them over any other phone I've heard and I know their sound inside out.  So I guess I'm just interested in source and DAC/amps where applicable.

If I can't get close to the kind of clarity I get at home, I'll stick with what I've got and live with being a bit disappointed with the sound, but you think there's anything I should check out, let me know.

I've read through so many reviews and forums on the internet, and they all say different things (and obviously none of them compare gear to gear I've already got) that I'm a bit confused as to where I should be looking.

Thanks 

So here are some ideas:

Fostex HP-P1 with an iPod Classic - Still keep massive storage of iPod and ease of use of iTunes to tag my WAVs, bypass iPod DAC, amp and signal flow completely, plus line-out to hook directly up to my Focals at home... sounds pretty good!

Upcoming iBasso DX100 - Looks good, but don't really know enough about it.

FiiO E17 with iPod Classic - Same as the HP-P1 i guess, but anyone know if the SQ is as good?  Also does this take digital direct from iPod to bypass the cheap apple components like the HP-P1 does and does it do line out to go to my Focals without needing anything else?

HifiMan - Not sure which model, or about these at all.  I like the idea of a nice warm sound, but my headphones are fairly warm anyway and so don't want to overdo it.  Also, even though I'm mostly interested in sound, I'm not sure I could live with a badly built UI, it would just take all of the joy away.  Also, no gapless play?????? Oh dear... but they are supposed to sound nice :)

Anyone comment on those, or any that I have missed?

Thanks, I hadn't really considered upping my phones.  I really don't like wearing IEMs, plus those are too pricey for me!  If I did up my phones to different set of headphones, any ideas on what I could go for, max $500?

Thanks guys, the Ultrasone's are a bit too pricey, £750 here in the UK, so must be over a $1000 in the US!  After doing some research, within my price range it has to be the HD25-1, the DT1350 (I'm a big fan of the DT sound, as you can tell by me sticking to DT250s for years!) or maybe even the Audio Technica M-50 (athough these are pretty big!).  

You guys are the second people to recommend the HD25 and the DT1350, so I must be on the right track!  Every review I've read loves the HD25, and also people are raving about the DT1350!  I just wonder if either will make a massive difference over my DT250?  New phones have to make a big difference  in SQ for me to bother i guess.  Will either of these two do that over the DT250?

So I'm quickly realising that I can't afford to get a really high end system, so I'll have to settle for middle of the road and maybe build it up gradually.

What I've decided to do, as I wasn't expecting to buy phones and my budget isn't endless, is to stay with the iPod and Walkman for now, get some better phones, see what difference that makes.  Then next get a half decent amp and then If I feel the need, look into getting a better DAC later down the line.  Do it gradually, spread the cost and also then I can really see the difference each bit of kit is making.

So what amp should I look at to come off my sources and into whichever of these phones I get?  I heard the