Cleaned out the closet over the past 3.5 months:
1. Brainwavz Alara: Nice bass, decent mids, recessed highs lacking any good traits.
3. HFM HE5LE: Remembered better than it was, too bright, too moody; mods don't really help.
3. MD 4XX: "FUN" response curve, OK for price for non serious listening. Son gets it for good this time. The midbass/upperbass is a sloppy mess w/o dynamat. Highs bright.
4. Fostex FH500RP: tried many mods, clean and unobjectionable. No bass push, treble too polite and lacking detail. Mids OK w/ female vocals. Relaxing but un-revealing.
Current list:
1. HFM HE6se 9.75/10.0: (mods: rear screen off, MrSpeaker Ether Angled Pads, fuzzor, dynamat, low impedance copper cable). Incoming power now steady at 120 VAC. TIDAL hi-res via LG V40, and toneboosters EQ have really added up to a stunner. Less bass impact than HE-6, but a steadier and more uncolored can across the board. Slightly brighter texture than the music, but much closer than stable mate Ananda or HEK v1. At $700 a bargain, even good at $900.
2. HFM HE-500 9.5/10.0 (Fuzzor, screens off, Ether Angled pads, Copper cable, dynamat); midrange first, bass and treble very good however, very wide soundstage, excellent depth, speaker like, bit warm but lots of detail. Classic. Thicker and slower than the 6se.
3. HFM HEX v2 9.45/10.0 (mods: Dekoni Nuggets to raise bottom of cups up to get max treble and detail). Lacks upper mids/treble drive/detail - until Toneboosters EQ. Now detail and drive restored. Also tone on vocals more correct w/ EQ. Very coherent overall sound - might be its calling card. Analog/vinyl like. Nice bass extension to 20 Hz, but the impact is diffuse. Tall but somewhat narrow soundstage an occasional bother. Not a classic, but memorable to those that want to bathe in the music.
4. Senn HD-600 8.9/10.0 (mods: dynamat, felt) this rating on Ragnarok 1, on BH Crack w/ speedball it's a 9.4 (bass erupts down to 32 Hz, and it gets an inner lighting/life that is a wonder to behold. For sure HD warms them up. Very liquid. Snigger all you like, until you hear it). Clean, tonally correct, great for classical. If it imaged like the 800, it would be lights out. Slays 650's and Shure/AKG/AT/Grados/Beyers by the score - IMO (not every single one, just almost all of them). Way classic. If it sounds thin and strained in the treble your 600 needs more current.
Advice: A used Schiit Mjonir 2 (w/ NOS classic tubes to your taste) and a used HE6se would make a killer pair;
Also the BH Crack w/ speedball and the Senn HD-600 for less money if a meh soundstage is OK for you;
Insane: HFM Jr amp (used $4.5k) & Voce cans ($2k used), still the best I've heard.