So, I got a chance to apply the Rastapants 2 configuration today. I already had acoustic foam on the driver-side of the baffle (over the clay) and Dynamat on the inside of the cups, so the changes for me were to
1) switch out the transpore (two layers) to stiff craft felt
2) close up the vents with electrical tape and cover it with acoustic foam (i previously left one slit open)
3) cover the reflex column on the back of the cup with acoustic foam
I actually ran out of Silverstone foam so I didn't get to cover the entire earside of the baffle with acoustic foam yet. However, I do have two layers of a half donut underneath the backside of the earcup.
Although this headphone did many things well, the one thing I could not shake was a slight bloom in the midrange. This caused a slight smearing, and vocals sounded a tad muffled. Mind you, when my mind got used to the sound, I didn't notice it. But switching from the LCDs to the T50RP, it is quite noticeable. The configuration I previously found worked the best (2-layers of transpore over drivers, all vents covered except one, acoustic foam on driver-side of baffle) in fixing this bloom was still not 100% satisfactory. Plus it sucked out all of the sub-bass. The funny thing is, I heard a stock T50RP, and the vocals did not sound nearly as muffled -- but they were shouty in addition to many other problems.
After applying the Rastapants 2 configuration, I'm happy to say this problem has been fixed for me (!!!!). What a relief that this midrange is finally much better defined, with greater sense of air between each element of the music. There seems to be a much more "pure" air chamber inside the cups for the drivers to work its magic, without reflections or weird air movements coming from the vents. In regards to the overall sound, everything sounds very cohesive, and all the different frequencies seem well-seated and natural.
After doing some quick comparisons to the LCD-2's, the most immediate thing that I notice is that the bass is much lower in the T50RP -- both in impact and in texture. On Fleet Foxe's "Helplessness Blues", when the kick drums hit, they do so with authority on the LCDs, while the Fostex remains polite. On James Blake's "Limit To Your Love", there is a bass line toward the end of the song that the Fostex barely picks up, while it is very prominent with the LCDs. However, listening to jazz recordings (Bill Evans's "Waltz For Debby" and Medeski, Martin & Wood's "Last Chance to Dance Trance"), the bass plucks are just as lively on both -- with the LCD having a good edge in impact and a slight edge in texture. But truth be told, I might even prefer the slightly more shelved down bass lines on these two acoustic tracks that the Fostex presents. This bass performance isn't surprising given the LCDs have a much bigger driver, and I'd say it is a much welcomed tradeoff given that the midrange sounds so right.
Other things that jump out, is that the LCD's have a bigger soundstage, and are airier. Given that these are open-backed, this shouldn't come as a surprise. If I were to sum up the overall presentation differences, while both definitely sound more similar than different, the LCD is more natural and visceral, while the Fostex is more neutral and analytical. With that said, this Fostex in its current state is an endgame closed headphone for me.
I definitely want to give it more critical listening, and apply some acoustic foam over the entire earside of the baffle before giving any more opinions. I want to write more in-depth comparisons with this likely "final configuration" of my Fostex, before I ship my LCD out again. I also might experiment with opening the vents a bit to infuse a bit more low-end body into the presentation (the few hip-hop songs I've tried on these sound a tad thinner than I'd like), but I'm afraid of smearing the midrange again. If that's the tradeoff, then I'd gladly leave it as is.
Thanks again to all of the work that mrspeakers has done and has shared with us.