Hey you found the right person to ask, though my time is a bit limited these days. Earlier I had demo units of all three variants of the Fostex TH-X00 (Ebony, Purpleheart and Mahogany), as well as owning the HP-100 original, then modded for a few years. These two headphones are at opposite ends of closed-back collection I would say, having hardly anything in common. The HP-100's do Isolation about 5x better than the Fostex, especially with the pleather Dekoni earpads, which also improve dynamics & soundstage somewhat. Vocals sound good on the two, but the Fostex are much more lush and vivid in the mids, and additionally have the ability to handle complex passages, which lacks on the Soundmagics. All 3 versions of the Fostex have better bass definition than the SoundMagics, as well as more natural / organic sounding mids.
But IMHO, that's where as far as the cookie crumbles with those Fostex over the SoundMagics. Overall the TH-X00 variants all have either too much bass emphasis or hyper-analytical treble, and they all seem to cause listening fatigue from the low and/or highs being overdone, and all being a quite 'colored' sound with isolation almost as low as an open-back.
Move on to my new recommendation:
Sennheiser HD-380 Pro... What,
380 you may ask? Yep it may have a lower number but this relic beast of a closed-back was actually just released in 2016 if I understand correctly. It's the darnest thing how I discovered them too... after several days at Japan's largest headphone stores in both Osaka and Tokyo, very literally trying at least 200 other closed-backs, I was initially the most impressed with the
Focal Spirit Classic. These are actually on my head right now and giving me immense enjoyment... balanced tonality (yet ever so slightly dark leaning), great impact, realism, etc. and now a tighter more detailed sound with an upgraded silver cable.
Thinking I've finally found my end-game after 10 years of trying and even more recently modding closed-backs, I was super impressed with the Focal Spirit Classic. So still curious for more comparisons I went back to audition a few last closed-backs, leaving me very impressed with the
Sennheiser HD-280. To me these were a hefty 90% of the Focal Spirit Classic, being very proper and true sounding with bass that reaches even deeper, yet soundstage + details a but less. But here's what changed everything with me & closed-backs: several posts I noticed saying that the HD-380 is even better than the HD-280. Well I'll tell you, the first few minutes of putting those bad boys on to audition, I was in as much disbelief at their sound in-person as I was when reading about their superiority... and boy is that the perfect word for them!!! Leaps and bounds better than every other closed-back I've heard from brand A-Z including all of the above mentioned (and yes, multiple times better than the HP-100 / 150) - dynamics that are immediate, realistic and snappy, details galore, bass going subterranean deep with what could be perfect definition, nice mids, well extended top-end and absolutely nothing overdone... except perhaps the soundstage! Wow that is a soundstage to write home about, nearly 'out of your head', though still in a closed 'can, which may be attributed to their angled drivers and HUGE size earcups. Finally, ISOLATION in spades because they clamp even more than all of the above headphones, though I've read this can loosen in time. Overall the HD-380 to me a massive win over all other closed-backs I've ever tried, save the Mr. Speakers Ether C Flow at around two grand. Both the HP-100/150's and Focal Spirit Classic are discontinued anyway, and even weider yet... the HD-380 Pro are the cheapest of these all.
...
...(just pray all goes well with the adapting lol! 
But we still love him. 
....CHEERS!...CJ
