Just another guy's opinion...take it for what it's worth...my 2 cents...YMMV...
I took yesterday off to mod a set of T50RP's to mrspeakers' specs but without the O2 pads. Today, I made my compairisons; in total, over 14 hours of modding and testing. My objective has been to get as close as possible to LCD2's for under $100, so $150 Stax O2 pads do not factor into my goal.
Dynamat is nasty stuff, hard to work, and very difficult to remove as you will see later. It took me 6 hours to measure, cut, and place Dynamat in the cups, Paxmate Plus over the Dynamat, plasticine in the baffles/around drivers and Paxmate over that, 2mm stiff craft felt over the drivers secured with rubber cement, and changing out Shure 840 pads more times than I want to count - these are very difficult to put on the Fostex cups!
FWIW, I also compared "limp" felt, naked drivers, 1 and 2 layers of 3M Transpore tape, and 1 layer of 2mm stiff craft felt from Michael's.
My comparisons were made between my:
1. Rastapants 2 (with stiff felt - soft side down; Shure 840 ear pads, not Stax O2 ear pads)
2. Stock T50RP
3. BMF (vanity plates) with plasticine baffles, Paxmate cups, stock bass port felt, stock white driver felt, Paxmate ring under stock ear pads vs no ring with Shure 840 pads
4. Shure SE535 in ear monitors
5. Audeze LCD2 - v1, second revision of pads and cables
Chain: MacBook Pro --> glass toslink to Dacmini --> Stock cables to respective phones
Lossless media files : Anna Maria Jopek-Upojenie; Diana Krall-My Love Is A Mountain Side, Dancing In the Dark, The Look of Love; Patricia Barber-Light My Fire, Too Rich For My Blood; Sade-Please Send Me Someone to Love; Rufus Wainwright-Slideshow; Radiohead-Jigsaw Falling Into Place, There There, You; Gorillaz-Dare, Clint Eastwood, Feel Good, Inc; Donald Fagan-Century's End, Babylon Sisters, Janie Runaway; k.d. lang-Wash Me Clean; Brahms 3rd Symphony 3rd movement; Bill Evans-Peace Piece
These tracks are challenging from bass to mids to treble consisting of jazz instrumentals; jazz vocals; alternative electronica, jazz-rock fusion, and classical.
1. Stock T50RP aren't bad but they are held back by resonance and reflections.
2. Dynamat is a royal pain and not worth the effort.
3. Rastapants 2 is very good but does not suit my ears. The sound is neutral but with veiled mids and highs; bass is very good, textured, and tight. They have an obvious narrow soundstage/closed- in sound to my ears compared to all the other phones in this set of my comparisons. This is not surprising to me since they are completely closed. Obviously, I have not and will not try the O2 pads. The excellent results mrspeakers achieved may be due to the synergy of his mods with O2 pads vs. different preferences, equipment, opinions, placebo effect, bias, etc...mine included.
4. I prefer the sound of my BMF, as described, with their (to me) better clarity and wider soundstage compared to Rastapants 2. So, I next removed the Paxmate and Dynamat over the bass ports, then tested and the result was improved soundstage and better mids/treble but with some bass bloom. Next, I removed the Paxmate and Dynamat over the center cup compartments and the result was more improvement to soundstage but a bit more bass bleeding into the midrange. The solution for me was to cover 3 of the 4 bass port slots with Paxmate (with the stock bass port felt in place) - Problems solved (for me).
5. After (conservatively) literally 100's of individual mods to 4 sets of T50RP's and countless hours of side-by-side comparisons, I have concluded:
* T50RP's can be improved
* Rastapants 2 is very good but I like my BMF's more because they satisfy my preferences just as mrspeakers tuned his to suit his preferences. There is no "right or wrong" way or "best" way. It simply comes down to personal taste, preferences, opinions, equipment, etc. That is why you can read everything about modding and a multitude of opinions but you will never know which is better for you until you try them for yourself.
* As good as I have been able to make them, and as good as they are for < $100 cans, modded T50RP's are no match for Shure SE535's and LCD2's. In my opinion, the LCD2's and SE535 are in another league with superior soundstage, deep-textured-controlled bass, clarity-space-and air, absence of bass bleed into the midrange, to die for mids, and transparent treble. SE535's give the LCD2's a run for the money. It is not surprising to me that the modded T50RP's (mine) have consistently been bested considering the SE535 has 2 bass an 1 treble balanced armatures per side and the LCD2 is open and 4 or 5 times the driver size compared to T50RP's. If I had never heard the SE535's and LCD2's, I would be very happy with my modded Fostex. In fact, I am very happy with them for their low price and very good sound, once modded.
* Simple is better. The easiest mods and best bang for the buck, as far as I am concerned, are Paxmate in the cups, plasticine in the baffles, stock bass port felt intact, Paxmate covering 3 of the 4 bass port vents on the inside of the cups, the baffle vents open, and a Paxmate ring under stock ear pads. For the trouble of putting plasticine in the little holes around the driver, the effort was not worth the results to me. For $15, Shure 840 pads offer a good upgrade (except for the difficulty of putting them on) and keep the total modded price under $100.
* Stiff felt is definitely better than limp felt.
* Stock white driver felt, 2 layers of 3M Transpore tape, and 1 layer of stiff craft felt are too close for me to tell a difference.
* Shure 840 pads are definitely better than stock, cost $15, and are a pain in the butt to put on - make this your last and final mod.
* Music straight from my MacBook Pro vs Dacmini is definitely different, favoring the Dacmini by a wide margin. Still, if I had never heard the Dacmini I would be happy with the MacBook Pro, alone. Yes, it can drive the modded T50RP's.
* Paxmate over baffle plasticine was not better than plasticine, alone, with my mods.
Mods and comparisons:
CEntrance Dacmini, Stock T50RP, BMF #4 mods, Rastapants 2 mods with Shure 840 pads, Audeze LCD2, Shure SE535, MacBook Pro.
Plasticine in baffles and Paxmate over plasticine. Electrical tape over bass port vents.
Dynamat in cups. Plasticine around drivers. Paxmate over baffle plasticine.
Paxmate over Dynamat. Driver waiting for stiff felt. I also tried limp felt, 2 layers of 3M Transpore tape, and naked drivers. Stiff felt is better than limp felt and naked drivers; and equivalent to stock white driver felt and 2 layers of 3M Transpore.
Stiff felt over naked drivers. Plasticine in baffles and around drivers. Paxmate over baffle plasticine. Stiff felt works - limp felt does not.
Stock set and Rastapants 2 with Shure 840 pads.
Stiff felt. Dynamat + Paxmate in cups. Removed Paxmate over baffle plasticine. Removed Dynamat and Paxmate over bass ports, stock bass port felt intact.
Rastapants 2 with bass port exposed by cutting away Paxmate and Dynamat. This opened them up quite a bit. As above, I kept the bass port felt in place.
Rastapants 2 with bass ports an central housing exposed by removing the Paxmate and Dynamat. This further improved soundstage. There was a bit of bass bloom into the mids corrected by placing Paxmate over 3 of the 4 felt-covered bass ports (not shown).