"Best" Closed Foldable/Portable headphones?

First off, I'm relatively new to the headphone world... I just got my first "big boy" headphones a couple months ago, Audio Technica ATH-A900's, along with a FiiO E7 portable amp/DAC. I couldn't be more pleased with them, I love the sound out of the box and feel no need/want to equalize them, they're comfortable, and I could listen to them all day. Before I purchased them I listened to a set of Sony MDR 7506's and couldn't stand their default sound. They were way too harsh/bright for me. I found them pretty fatiguing, hard to listen to for more than 30 minutes for me.

So, with that in mind, I've done some research on the forums here, googling, etc and *think* I have things narrowed down. I've eliminated the HT-21's since they've been said to be pretty bright/harsh.

So right now, I have it mostly down to the AKG K450, AKG K518, and Soundmagic P30. If you guys have any suggestions outside these, the price should definitely be <$100. The K450's are already ~$90 with shipping from amazon. That's getting close the the ATH M-50's at $135. The M-50's aren't really as portable as I'd like though. However they're a set I've heard a lot of good things about, and I'll eventually be getting a set, but I'm not too sure how different they sound compared to my A900's.

I'm guessing the K450, K518, and P30 all more or less need some type of amp? I tried my A900's without an amp on my iPod touch and the distortion at listenable levels was pretty bad, to the point I'd rather listen to $10-15 earbuds if I didn't have an amp.

I'll mostly be listening to various kinds of rock (hard rock, instrumental, post-metal, post-rock, progressive, psychedelic, etc), as well as ambient, and electronic.

Those Koss phones look a bit bigger than I'd like for a portable set, I'd probably just go for M50's if I were to get something that big. I'll likely just get a FiiO E6 with whatever I decide on for something more portable than the E7, and keep the E7 at home with the A900's.

Did some more browsing on specific reviews on those sets here on the forum and it looks like the K518's clamp pretty tight. Seems some users have said the audio quality on the K450 isn't great, but others say it needs to be burned in... That makes me lean towards the P30, but between that and the K450 it seems like a bit of a toss-up.

*EDIT* - Oh, and there's also the Audio Technica ATHES55BK, but I can't seem to find hardly any info/feedback on them.

Not for now. I tend not to use in ear phones unless I'm at the gym/doing something very active where normal phones would fall off, generally that involves sweating too, which cause problems for in-ears. I've gone through probably 4-5 sets of cheap Sony's from active use. Surprisingly my current set's lasted a year or two though. Comfort wise, In-ears bother me after ~1-2 hours. These are mostly going to be for when I travel, and I don't want a huge set like my A900's, or something like an M50. It'd be used at the airport, hotel room, walking around the city, etc. They would also be a secondary headphone set for my 2nd PC when guests use it, so in ears won't really fit the bill too well for that.

Still fairly undecided between the Audio Technica ES55, AKG K450, and Soundmagic P30. The one thing I don't like about the ES55 is each cup has a wire coming from it. The K450 seems like it has the best retail package as far as the case it comes with, etc, but I'm not sure if the detachable cord on it is a good thing or a bad thing. Seems like it might be a component that could fail, and it's a proprietary cable, so replacements are relatively hard to get.