Weird...I just ordered a pair a couple days ago exactly for modding purposes after a few years of eyeballing them.

^Nah, makes it worse. The HM5 pads were stretched out from the larger T50RP housing, so the fit is kind of loose. The poor seal gives it an open-back type presentation which I like. Also, the worse the seal against my head, the more I like the sound.

I also tore off the grille fabric from the pads a la Abyss. TME, this allows more detail to come through. Still amazed at what I'm hearing independent of the price.

At about 200 g with plusher pads, easily the most comfortable cans as well.

No, Amazon is failing pretty hard with my order because it contains a 2nd headphone that's technically from a different seller. Order was supposed to arrive today, but on closer inspection, Amazon shows they still haven't even shipped the order. To them, I say

Finally got mine in yesterday. Spent some time listening and modding over the night. They really are not bad. A little cheap feeling, but comfortable and lightweight. I have only tried the stock pads, but I could see the HM5 pads working well. I am considering ordering a pair.

I don't mean for this to be a pun, but I'd say they have a lively sound. The bass cleans up pretty nicely after some simple mods, but it's still bassy. Something about them is a little hollow and scooped out sounding, but not terribly so. So far, they sound fairly detailed but not too fatiguing, a nice change from what I remember with the D2000. Something about them is still a bit artificial sounding. There's either a small emphasis or a bit of ringing somewhere in the treble, but it only comes up in certain recordings and even then not all the time. It's more of a curiosity than anything and surprisingly didn't bother me too much right away.

Good or bad regardless, they're pretty involving and a good listen. I might still like the modded Tascam TH-02 a bit more. Even with mods, it costs less than the stock CAL!, though perhaps the HM5 pads would make a large difference on the CAL! like they did for the TH-02. I also got the Logitech UE6000 in at the same time. They're about $20 more than the CAL!, and I think they're pretty darn close in terms of good sound for value if you didn't want to mod either the CAL! or TH-02.

Sold mine eventually.

It had a 'PortaPro' factor (as I call it, doesn't mean it sounds like one in the least) in that they are easily to 'tune' into without exhibiting annoying faults and sound totally believable although you do hear it isn't a top tier headphone.
The presentation is 'nice' and warm/full bodied, no piercing treble no immediate sense of rolled off highs.

Strange part of them is (just like the PortaPro does) that when you listen to them exclusively it does not make you 'wanting' to put on another headphone, yet when you swap it for a 'better' headphone and go back to it from that better headphone after a short while you immediately hear where it is lacking.
Also found the peak in the treble and mushy bass annoying after a while but did not do any mods to it (except some felt in the cups and wool but did not help that much).

Sold it in the end because it got no headtime any more also because it gave me 'warm ears' rather quickly.

Nice headphone and could recommend it for 'easy to adopt to' reasons alone.
IMO this 'easy to adopt to' makes a headphone successful.