I will be plugging them in to a portable amp iBasso D4.

Really, make sure you TRY ON the Fostex before buying them. Pro Audio shops will have'em and will probably have a demo set of the models you're considering. The Fostex have what I'd call a design flaw with the earcups pressing on the user's earflaps. I couldn't get rid of mine fast enough. Watch out.
The Thunderpants will be the modded Fostex T50RP, can't wait to give them a listen.

volume wrote"
I would probably want to stay away from IEMs.
Why no IEM's? You do know a decent set of IEM's, dollar for dollar, in their own way, kick headphone butt? FWIW, the main headphones are a set of Sennheiser HD650's.
Currently listening to a newly arrived set of refurbished Sennheiser IE8's I picked up on Amazon for $186.00 delivered.
The idea behind the IE8's was so I wouldn't need an outboard Amp to get decent sound when using the Sansa Connect. I must say, the IE8's, for the refurbished price, hit it totally out of the park.
???
With IEMs,I don't know what the customs would sound like, and don't want to spend that much in order to try,apart from that the IEMs give you all the details in the music and more, but the headphones give you that fiuller sound which I 'am addicted to from my home rig.

My favorite completely neutral phone is the Koss Pro DJ 100. They need an amp, but they're my favorite for the types of music I like. They're only $80 and I just today found out that work with the Pearstone Velour pads, but you need to stretch them a bit. Those pads are about as comfortable as Beyer pads. I can now wear them all day if I wanted. Comfort is just amazing now and it doesn't degrade the sound quality.
Some pairs of these headphones sound bad out of the box and need a ton of burn in. My first pair was perfect, but my second pair needed 24-48 hours of burn-in. I almost felt I had a bad pair. After burn-in the mids are more forward, but the bass is slightly reduced. This made me a believer of burn-in! Complete difference.
For ME these have the best mids out of everything i've tried. They have bass, but there is not a lot (WAY more then the RE0 and AD700. They're not bass light). It's a tad less then what the SRH-840 has. The highs are VERY slightly rolled off, but this is what I prefer. Not as much as the HD-600 though.
I prefer these for my music over the M50, SRH-840 and pretty much every headphone i've tried. I'm probably up to about a dozen of them.
They're bad for rap, metal and some classical though I imagine. I find them to be the perfect headphone for female vocals. Pearl Jam, Imogen Heap and Radiohead sound amazing on them. Especially Thom Yorke's "The Eraser".
The level of detail is really good. About the same as the SRH-840, but not the AD700.
I also love the SRH-840, but it won't fit my small head or I would have kept them.
Maxell DHP-II is also great and doesn't sound like a $28. Most people will see that price and just pass them off as junk. They sound better then a lot of $100 headphones. It has more bass then the Pro DJ 100 but isn't as neutral.
Thanks for the recommendations and sharing your observations, this is the way we all learn.









